Diversity, Relative Abundance and Some Aspects of the Biology of Fishes below the Tisisat Fall of the Blue Nile River, Ethiopia
Tadlo Awoke Mengesha
Department of Animal Production and Extension, Gondar, Ethiopia
Publication Month and Year: November 2019
E-BOOK ISBN: 978-81-944644-2-6
C-11, 169, Sector-3, Rohini, Delhi, India
This thesis work could not have been successful without the contribution of many individuals and institutions. I have no words to express my deepest gratitude and sincere appreciation to my research advisors, Dr. Minwyelet Mengist from Bahir Dar University; Fisheries, Wetlands and Wildlife Management Department, and Abebe Getahun from Addis Ababa University for their unreserved scientific advice, guidance and the accomplishment of this study. Their critical constructive comments starting from the proposal until the thesis writing and supply of related literature facilitated the smooth completion of this study.
Indeed, it is quite difficult to me to express my internal feeling with the languages I know so far to acknowledge Dr. Minwyelet Mengist contributions to the realization of this study. He was seriously committed right from the beginning by suggesting the research area. He was also supplied me the necessary field materials in time. He is so friendly and has helpful attitude, which I consider it was an important quality.
I am grateful to the staff members of the Bahir Dar Fish and Other Aquatic Life Research Center for their technically assist during my filed and allow the laboratory works. Especially Biniam Hailu and Temesgen for their support in both the field and the laboratory work.
I would like to thanks Bahir Dar University for Budget and logistic support, which is required for fieldwork for my thesis. I am grateful to my friends Shewit G/Medium and Marcos Buddha for their hospitality and encouragement in my two-year stay and in accessing their computer.
My due thanks go to my family, especially my father Awoke Mengesha and my mother Fenty Teshager their sympathy and sensitive follow up while I was in fieldwork.
Finally yet importantly, peoples of Fich, Angar and Wazir Ki Bela and Amhara National Regional State police commission working are duly acknowledged for their unreserved efforts in providing valuable information and support letters for the study.
Almighty god, thank you! You make everything possible for me. Save my family and help me to realize my dreams.
S. No.ChaptersPage No.
1.1Freshwater bodies in Ethiopia01
1.2Fish species diversity in main drainage basins of Ethiopia02
3.General Description of the Study Area08-13
4.Materials and Methods14-18
4.1Site selection and sampling14
4.3Species diversity and relative abundance15
4.4Shannon index of diversity (H')16
4.6Condition Factor (Fulton Factor)16
5.Results and Discussion19-39
5.1A biotic Parameters19
5.2Fish species composition in the upper part of Blue Nile River20
5.2.1Diagnostic and descriptive characteristics of fishes23
5.2.2Species diversity and abundance27
22.214.171.124Relative abundance of fish during wet and dry seasons29
126.96.36.199Length frequency distribution of the dominate fish species33
5.3Some biological aspects of the dominant fish species34
5.3.2Fulton’s condition factor (FCF)36
5.3.3Some aspect of reproductive biology37
6.Fishing Activity and Its Problems in the Study Area40-42
6.2Problems in fishing activities42
7.Limitation of the Study43-43
8.Conclusion and Recommandations44-46
List of Tables
Table No.TablesPage No.
1.Number of fish species and endemic species in the main drainage basins of Ethiopia05
2.Sample sites and there codes, estimation distance from the Tisisat fall elevation, habitat, width of the river and coordinates10
3.Macroscopic description of various gonadal stages17
4.A biotic parameters in the sampling sites with their Means ±SE in both dry and wet seasons (Mann-Whitney U test)19
5.Fish species composition and local name in amharic according to the local people20
6.Fish species presence in sampling sites (present, +, absent, -)21
7.Fishes specie composition compression above and below the Blue Nile Fall (+, present and -, absent)22
8.Fish distribution among the sampling sites both dry and wet seasons (+: present; -:absent)27
9.Shannon diversity index (H') and number (N) of fish species in dry season28
10.Shannon diversity index and number of fish species in wet season28
11.Number and total biomass (kg) of fish during wet and dry season29
12.Species number and percentage composition of both in dry and wet season in sampling sites (One way ANOVA)30
13.Percentage index of relative importance of fish species in dry season31
14.Percentage index of relative importance of fish species during wet season31
15.Pooled catch of IRI and H' values in both dry and wet seasons at all the sampling sites33
16.Mean and Standard deviation of Fulton condition factor both by sex and season: P= significance difference (Mann-Whitney U test) between sex and seasons of dominant fish species36
17.Number of males, females and the corresponding sex ratio38
List of Figures
S. No.FiguresPage No.
1.Map of study area09
2.Mean maximum and minimum air temperature11
3.Mean monthly rain fall12
4.Lateral view of Labeobarbus intermedius23
5.Lateral view of Labeobarbus crassibarbis24
6.Lateral view of Labeobarbus nedgia24
7.Lateral view of Clarias gariepinus25
8.Lateral view of Mormyrus kannume25
9.Lateral view of Bagrus docmak26
10.Lateral view of Labeo forskalii26
11.Lateral view of Oreochromis niloticus27
12.Shannon diversity index (H') and Number of fish species in both dry and wet seasons28
13.Percentage IRI of dominant fish species in sampling sites during dry and wet season32
14.Length frequency distribution of L. intermedius34
15.Length-weight relationship of L. intermedius, L. forskalii and M. kannume respectively36
16.ABC Absolute fecundity with total length, total weight and Gonad weight relation in L. intermedius39
17.Farmers fishing time in the study area41
Chapter - 1
1.1Freshwater bodies in Ethiopia
Ethiopia is water tower of East Africa and has a number of lakes and rivers in which the majority of the rivers and lakes are situated in Rift Valley of Africa (Leykun Abunie, 2003). There is about 7,000 km length of flowing (rivers and streams) and 7, 400km2 area of standing waters 7,700 km2 (MOA, 2003). In addition, minor water bodies such as crater lakes and reservoirs make up about 400km2 area (Tesfaye Wudneh, 1998).
The main drainage basins of Ethiopia flow away from the rift system either towards the Nile system in the west or to the Indian Ocean in the southeast. Ethiopia has seven drainage basins that include Abay, Awash, Wabeshebelle-Ghenale, Omo-Gibe, Baro-Akobo, Tekeze and Rift Valley basins (Mesfin Wolde Mariam, 1970): which can be categorized under three main drainage systems.
The first drainage system is the western drainage system, which includes the sub-drainage systems of Baro-Akobo, Blue Nile and Atebara-Tekeze. Rivers Didessa, Dabus, Beles, Gelgel Beles, Beshilo, Dura and Ardi are tributaries of the Blue Nile that drain the southwestern parts of the western highlands of Ethiopia (Abebe Getahun and Stiassny, 1998).
The second drainage system is the Rift Valley system, which is composed of awash sub-drainage system that drains in to Lake Abbe, at the Ethio-Djibouti border and it is a closed system. Omo- Gibe sub drainage system flows to the south to Lake Turkanna (Rudolf) at the border with Kenya. The Rift Valley Lakes are again categorized into three-sub system on the bases of the similarities of their fish fauna. These are Southern Rift Valley Lakes (Chamo, Abaya and Chew Bahir), Central Rift Valley Lakes such as Hawassa, Shalla, Abijata, Langeno and Ziway (LFDP, 1996) and the Northern Rift Valley lakes such as Afambo, Gamari, Afdera, Asale, and parts of Abbe.
The third main drainage basin is the Wabi Shebelle-Juba drainage system. It is composed of sub-drainage system of Ghenale, Dawa and Weyb Rivers that join Shebelle River and drain to southwestern parts of the eastern highlands. The Wabi Shebelle River is called Juba in Somalia. The major rivers in this drainage system arise from the eastern highlands in the Bale Mountains of Ethiopia and flow into the Indian Ocean (Roberts, 1975).
Four major river systems originate in the Ethiopian highlands. The Awash arises in Shoa and flows northwards following the Great Rift Valley where it disappears in the desert near the Djibouti border. The Omo begins in Kafa and drains into Lake Turkana, in the south, on the border with Kenya. The Wabi Shebelle originates in the Bale Mountains and flows in a southeastern direction towards Somalia. The most impressive river, however, is the Nile, which flows MOR than 6,000 km from its source (Lake Tana) to the shores of the Mediterranean (De Graaf, 2003). The Nile River is principally fed by two great rivers, the White Nile and the Blue Nile, which fuse at Khartoum, Sudan's capital city.
1.2Fish species diversity in main drainage basins of Ethiopia
Ethiopia has a rich diversity of ichthyofauna in its lakes, rivers and reservoirs, although they are poorly known (Abebe Getahun and Stiassny, 1998). Even though, Ethiopian has high production potential and notable fishery investigation has been carried out only in a few of numerous freshwater bodies. The territory of Ethiopia encompasses parts of the catchment areas of two oceans, separated by the north portion of the Great African Rift. Two major biogeographic units, the Nilo-Sudan and the east coast ichthyofauna provinces are in contact to this region (Golubtsov et al., 2002).
Shibru Tedla (1973) has listed 94 species of fish in Ethiopia. Although extensive review work is in progress, it appears that there are 153 valid indigenous fish species included in 25 families in Ethiopia freshwater (Abebe Getahun, 2002). According to Golubtsov and Mina (2003), the total number of valid species in Ethiopia inland waters is about 168 to 183 including 37 to 57 countrywide endemics. There are also 10 exotic fish species introduced from abroad into Ethiopian fresh waters (Shibru Tedla and Fisseha H/Meskel, 1981). Currently results of various studies indicate that the number of fish species could increase to 200 and above (JERBE, 2007).
The freshwater fish fauna of Ethiopia is a mixture of Nilo-Sudanic, East African and endemic forms (JERBE, 1995; Abebe Getahun and Stiassny, 1998; Abebe Getahun, 2007). The Nilo-Sudanic forms are represented by many representative species. For example, the genera Alestes, Bagrus, Citharinus, Hydrocynus, Hyperopisus, Labeo, Malapterurus, Mormyrus, Polypterus and Protopterus are some of the representatives from Baro Akobo, Omo-Gibe and Abay basins. The Nilo-Sudanic forms are related to West African forms and are believed to occur here due to past connection of the Nile to Central and West African river systems. According to Abebe Getahun (2002), some of the elements of Nilo-Sudanic species are reported from southern rift valley lakes (Chamo and Abaya). These include the families Mormyridae, Cyprinidae, Bagridae, Clariidae and Mochokidae. Wabi Shebele and Jube basins also have element of Nilo-Sudanic forms.
The highland East African forms are found in the northern rift valley lakes (Lake Awassa, Ziwai and Langano), highland lakes (Lakes Hayq and Tana) and awash drainage basin. The genera include Labeobarbus, Clarias, Garra, Oreochromis and Varicornis. They are related to fishes of Eastern and Southern Africa and Arabian Peninsula (Skelton et al., 1991).
Fish fauna of Ethiopian high lands are dominated by species of fish in the family Cyprinidae (Roberts, 1975). The fishes of the high mountain torrential streams largely belong to Cyprindae (Abebe Getahun and Stiassny, 1998) adapted to the swiftly flowing floodwaters that occur seasonally. Two genera of fishes (Barbus and Garra) are dominant in these streams. It appears that there is high endemism of fish, but fauna is not well known. Endemic fishes of the genus Garra (e.g. G. dembecha, G. duobarbis) have been described recently (Abebe Getahun, 2002). Some of endemic fish species are found in Abay basin: Labeobarbus zephyrus Boulenger 1906, V. beso and some Garra species (Golubtsov and Mina, 2003).
Some of the family of fish identified within the Nile basin and its tributary rivers are Mormyridae, Characidae, Cyprinidae, Bagridae, Schilbeidae, Mochokidae, Clariidae and Cichlidae (MoWR, 1998). Moges Beletew (2007) assessed fish diversity in Beshilo, Ardi and Dura Rivers of Abay basin and found twelve species of fishes. These represent by five families i.e. Cyprinidae, Clariidae, Bagridae, Mochokidae and Cichlidae. Some of the species were L. intermedius, L. nedgia, C. gariepinus, V. beso, O. niloticus, S. schall, R. loti, B. docmak, B. bajad, L. forskalii and H. longfillus. According to Zeleke Berie (2007) a total of 22 species of fishes were recorded from Beles and Gelgel Beles Rivers of Abay basin. Seven families represent these: Cyprinidae, Clariidae, Bagridae, Mochokidae, Characidae, Mormyridae and Cichlidae, represent these.
There is no clear, complete list and description of the diversity of the fish fauna of Ethiopia. Many of the drainage basins especially the rivers are not exhaustively explored (Abebe Getahun, 2002). There are 38 endemic species and sub species to Ethiopia (Abebe Getahun, 2005a). Lake Tana from Abay drainage basin exclusively has large number of endemic fish species in the country (Abebe Getahun, 2005a).
The Abay basin is one of the tributaries of Nile and consists of 36 species (Abebe Getahun, 2007) of fish of which 23 are endemic (Golubtsov and Mina, 2003; Abebe Getahun, 2007). Most of the endemic species of Blue Nile basin occur exclusively in Lake Tana. Lake Tana is a lake in the northern high lands of Ethiopia and is the source of the Blue Nile. The Blue Nile descends from Lake Tana to Tissisat Falls (ca. 40 m high), effectively isolating the lake’s fresh water fauna from the rest of the Nile (Thieme and Brown, 2007). It was formed by a volcanic blockage that reversed the previously north-flowing river system. The isolation of the lake from all but in flowing rivers has led to an endemic freshwater biota. Fish species in the lake are most closely related to those of the Nilo-Sudan biogeographic region.
Seventeen species of large barbs have been described from Lake Tana (Nagelkerke & Sibbing, 1998 & 2000). Eight of the large barbs are piscivorous, and Barbus humilis and the newly described, Barbus tanapelagius, are thought to be the major prey species (de Graaf et al., 2000).
About 70% of the fish species in this highland lake are endemic, including 20 endemic Cyprinids. The tilapia of Lake Tana belongs to a wide spread species but is described as an endemic subspecies, Oreochromis niloticus tana (Eshete Dejen, 2003; Thieme et al., 2007).
The family Cyprinidae is the only group of fish that is more diverse in the Blue Nile drainage system than in White Nile system. All other forms occurring in the latter system are represented by few species or absent in the former system. This might be the lack of flood plain in the Blue Nile system as was suggested by Golubtsov and Mina (2003).
According to Golubtsov and Mina (2003), the fish diversity in Atbara-Tekeze is less in comparison with Blue Nile and White Nile due to accessibility in the former system. JERBE (2008) reported 34 fish species belonging to 10 families and 22 genera from Atebra-Tekeze basin system. That means two to three times fewer species than Blue Nile and Whit Nile system respectively. The JERBE recorded 22-23 fish species from Abaya-Chamo system, 12-14 fish species for Chew Bahir, 12 species for Zwai-Langano, Abijata-Shalla system, 6-7 fish species for Awassa-Shalla system and 13-25 fish species for Awash and its adjacent enclosed basins (Golubtsov and Mina, 2003).
The highest fish diversity recorded, among Ethiopian main drainage basins, is from the Baro basin. According to Golubtsov and Mina (2008), 113 fish species belonging to 26 families and 60 genera were recorded from Baro-Akobo basin. However, the basins are low level of endemism as compared to other Ethiopia drainage basins. Low level endemism is probably because of the Baro basin have connections (past and present) with the Nile and West and Central African river systems and as a result of all the fish fauna represent widespread Nilo-Sudanic forms (Abebe Getahun, 2007).
According to Golubtsov and Mina (2003), 33 fish species belonging to 12 families and 21 genera were recorded from Wabi Shebelle and Juba drainage basins within the limits of Ethiopia. This region is inhabited by most distinct ichthyofauna within the country. A number of East African fish taxa occur in this basin such as the Characid Alestes affinis, the Cyprinid, Neobola bottegoi, the Schilbeidae irvine orientalis, the loach catfish Amphilius species, the Cichlid Oreochromis spilurus. There are 2-3 introduced fish species in this drainage system (Golubtsov and Mina, 2003).
The highest fish species diversity in Ethiopia has been recorded from Baro basin, followed by Abay, Wabi Shebelle and Omo-Gibe basins. However, endemicity seems to be highest in Abay and Awash basins. This is attributed, in the former case, to the endemic species flock of Labeobarbus in Lake Tana (Abebe Getahun, 2002) (Table 1).
Table 1: Number of fish species and endemic species in the main drainage basins of Ethiopia (Abebe Getahun, 2007)
Rift valley lakes327
Drainage basins No. of species No. of endemics species
Knowledge on diversity, population structure, distribution and population of the Ethiopian ichthyofauna and biology of fish species has been poorly known: relatively a number of small, medium and even some large rivers have not been well studied and explored (Abebe Getahun, 2005b). Therefore, further study on rivers is a time demanding phenomena. Blue Nile River originates from Lake Tana and flows down approximately 35 km in the southeast direction where it forms the famous Tisisat falls. This river especially below the fall has not been given adequate attention with regard to the study of the diversity, abundance and biology the fish fauna due to the presence of some harsh geographical features, inaccessibility for transportation, security and logistic problems. The purpose of the study is, therefore, to answer the following research question with the objectives mentioned.
•What is the fish composition of the Blue Nile River below the Tisisat fall?
•Do species vary in their relative abundance?
•What are some aspects of the biology of the dominant fish species found in this river?
•Is there some fishing activity around this river?
Chapter - 2
Major objective of the study is to generate baseline scientific information about fish species found in upper part of Blue Nile River below the “Tisisat” fall for management and sustainable utilization of the fish resources and recommend ways of conserving the diversity of ichthyofauna of the River.
•To identify fish species composition of the Blue Nile River below the Tisisat fall.
•To assess relative abundance of fish species in the river.
•To determine some aspects of the biology (Length-weight relationship, Condition factor, Sex ratio and Fecundity) of the dominant fish species.
•To investigate the fisheries activities and recommend appropriate resource utilization strategies.
Chapter - 3
General Description of the Study Area
The Nile River is the longest in Africa and the second longest in the world. It flows 6,700 km from its source in the equatorial lake basin to the Mediterranean Sea north of Cairo, Egypt. In between, it receives flows from a major tributary, the Blue Nile from the Ethiopian highland plateau, which contributes significantly to the Nile River’s total annual flow of almost 84 billion m3 per year at Aswan, Egypt (UNECA, 2000). The catchment area of over 3 million km2 of the Nile cuts across ten African countries namely, Burundi, the Democratic Republic of Congo, Rwanda, Tanzania, Kenya, Uganda, Ethiopia, Eritrea, Sudan and Egypt. This catchment area represents over 10% of the total land surface area of the African continent. The sources of the Nile are located in humid regions of Ethiopian highlands and the Great Lakes of East-Central Africa with an average rainfall rate of over 1,000 mm per year (UNECA, 2000).
The out flow from Lake Tana is the main source of Blue Nile River. The Blue Nile River flows the Eastern outskirts of the city of Bahir Dar at the Southern end of the Lake Tana flows down approximately 35 km in a southeast direction where it forms the famous Blue Nile Fall to drop in to a gorge having a depth of about 45 m (Yihun Dile, 2009).
Blue Nile River basin lies in the west of Ethiopia between latitude 7°45' and 12°45' N, and longitude 34° 05' and 39°45' E (MoWR, 2010). River Didissa, Dabus, Beles, Gelgel Beles, Beshilo, Dura and Ardi are tributaries of Abay (Blue Nile) that drain the southwestern parts of the western highlands of Ethiopia (Abebe Getahun and Stiassny, 1998). The Bashilo rises near Magdala and drains eastern Amhara; the Jamma rises near Ankober and drains northern Shoa; the Muger rises near Addis Ababa and drains south-western Shoa; the Didessa, the largest of the Abay's affluents, rises in the Kaffa hills and has a generally south-to-north course; the Dabus runs near the western edge of the plateau escarpment. All these are perennial rivers. The right rising mostly on the western sides of the plateau have steep slopes and are generally torrential in character. The Beles, however, is perennial, and the Rahad and Dinder are important rivers in flood-time.
Blue Nile basin shares common boundaries with the Tekeze basin to the north, the awash basin to the east and southeast, the Omo-Gibe basin to the south, and Baro-Akobo basin to the west (MoWR, 2002). The total area of the basin is 199,812 km2 including Lake Tana which has an area of about 3200km2. About 46, 31 and 23% of the total basin area falls in Amhara, Oromiya and Benishangul-Gumuz, respectively (MoWR, 2002). The River basin’s elevation ranges from 500 m to 4261 m and the total mean annual flow from the River basin is estimated to be 54.8 billion m3 (Seleshi Bekele et al., 2007).
The study was conducted in the upper part of the Blue Nile River (Starting from the Blue Nile Fall/Tissisat Fall to the border between East and West Gojjam). It lies between West Gojjam and South Gondar zones, specifically the adjacent Kebeles are Tis Abay, Wajir, Anigar, Gibish, Fichi and Dibaye (Figure 1).
Fig 1: Map of study area
Source: GIS Case Team Bureau of finance and economic at Bahir Dar
Table 2: Sample sites and there codes, estimation distance from the Tisisat fall elevation, habitat, width of the river and coordinates. Here on wards, Se, Ab and Wm refers to the sampling code
SiteCodeDistance (km)ElevationHabitatWidthCoordinate (GPS)
SefaniaSe81548mClear water and rocky, sandyMedium110 27.7' 07" N
37 37.9' 60״ E
AbenazeAb301528mTurbid muddyWider110 24.3' 06'' N
370 40' 71'' E
WotetomiderWm601493mClear water and rock gravelMedium110 31.5' 03" N
370 72.9' 48" E
According to Conway (1999), the local climate classification in Ethiopia is based on elevation and temperature. In other words, depending on elevation for any area there is associated mean annual temperature range. This enables identifying traditional climate zone of a given area. The three traditional climate zones of Ethiopia are: Kola (elevation less than 1800 m A.M.S.L and mean annual temperature 20-28 oC), Woina Dega (elevation between 1800 m and 2400m A.M.S.L and mean annual temperature 16-20 oC), and Dega (elevation between greater than 2400m A.M.S.L and mean annual temperature 6-16 oC). Based on the above local climate classification the climate zone of the study area is Kola (elevation is less than 1800m A.M.S.L).
The maximum and minimum mean monthly air temperatures of upper part of Blue Nile basin are 26.29 oC and 10.78 oC respectively at the Adet station and 25.39 oC and 11.31 oC at the Bahir Dar station (Fig. 2). The mean monthly rainfall was 141.5 mm at Adet station and 105.22 mm at Bahir Dar station. The main rainy season of this basin is between May and end of October (Fig. 3).
Fig 2: Mean maximum and minimum air temperature (a) at Adet station and (b) at Bahir Dar from 2006- 2010 (Ethiopian Meteorological Agency, Bahir Dar Branch, 2011)
Fig 3: Mean monthly rain fall (c) at Adet station and (d) at Bahir Dar station from 2006-2010 (Ethiopian Meteorological Agency, Bahir Dar Branch, 2011)
Blue Nile River below the Tissisat fall besides fishes there are other vertebrate animals found in the river. These are Crocodile, Snakes, “Arjano” (Monitor lizard) and different species of amphibians and birds. Species of birds observed during the study period were Cattle egrets (Bubulcus ibis), Great white pelican (Pelecanus onocrotalus), Grey heron (Ardea cinerea), Sacred ibis (Threskiornis aethiopicus) and African Jacana (Actophilornis africana).
There is high deforestation in the Blue Nile River basin below the Tissisat fall mainly hillside farming is devastating the forest and soil. Farmers in this area cultivate two crops a year and perennial crop farming is practiced. The changes in vegetation patterns result from land degradation along the Blue Nile basin below the Tissisat fall that may lead to unexpected abnormal floods and reducing soil nutrients of the basin. The other factors that a lead to deforestation is because of all of the residents do not have access to the electricity. The people use kerosene lamp and fuel wood as a source of light and for cooking. Therefore, the villagers continue to denude the remaining shrubs and trees for their daily consumption. Shrubs and trees mainly cover vegetations on either side of the riverbank. The dominant trees are Syzygium guineense (“Dokma”), Mimusops kummel (“Eshe”), Olea europaea (“Woyira”) and Ficus (“Shola”).
Chapter - 4
Materials and Methods
4.1Site selection and sampling
A reconnaissance survey was conducted to fix the sampling sites. The survey was conducted in three woredas along the River. Three sampling sites were selected taking into consideration; the velocity of the flowing river, interference by human beings and other farm animals, substrate type of sediments and accessibility, depth of water, and access to road. These sub areas are namely; Wotetomider site found in Wotetomider village at Fichi kebele, which is about 60 km down stream of Blue Nile fall, Abenaze site found in Abenaze village at Anigar kebele, which approximately 30km far from Blue Nile fall and Sefania site found in Wojir kebele, which is approximately 8km far from Blue Nile Fall. These sites were found in West Gojjam Zone under three woredas namly Gonje Kolela, Yelmanadensa and Bahir Dar Zuria, respectively. Data on fishing activity were collected using semi-structured questionnaires (Appendix 10.3). Conductivity, temperature, pH, Total dissolved solid (TDS) were measured using standard multi -meter and transparency was measured using secchi disk 20 cm in diameter. In addition to this cast, net was used in unsuitable areas of the river. Fish samples were collected in both wet season (November 2010) and dry season (March 2011). Each site was sampled two twice (one time in the wet season and one time in the dry season). Samples were collected using gillnet of various mesh sizes (6, 8, 10 and 12 cm stretched mesh) and monofilament nets with various stretched mesh size (5, 10, 15, 20, 25, 30, 35, 40, 45, 50 and 55 mm). In all studied sites, monofilaments were set during the daytime for two hours. Gill and monofilament nets were set, using swimmers, across the width of the river during dry sampling period when the water volume is less and parallel to the river flow during wet season when the water discharge is high. Gillnets were set late in the afternoon and collected in the water for 14 hours at deeper parts of the river and collected in the following morning. Cast net was also used by selecting an appropriate site. Immediately after capture, a gentle pressure was applied on the abdomen to check whether reproductive maturity has occurred or not. Then total length, fork length, standard length, total weight and gonad weight of all specimens of fish were measured to the nearest 0.1 cm and 0.1 g precision for length and weight, respectively. Picture of fish specimen was taken for each species. After dissection, gonad maturity of each fish specimen was identified using a five-point maturity scale (Nikolsky, 1963). Four specimens were preserved by 5% formalin from each species and transport to Bahir Dar Fish and Other Aquatic Life Research Center for morphometric study and comparison with previously identified specimens available.
Specimens were soaked in tap water for one day to wash the formalin from the specimens and then specimens were identified to species level using taxonomic keys found in Boluenger (1909-1916) and Golubtsov et al. (1995). The specimens were also compared with previously identified specimens, especially Labeobarbus species, available at Bahir Dar Fish and Other Aquatic Life Research Center.
4.3Species diversity and relative abundance
Estimation of relative abundance of fish was made by taking the contribution in number and weight of each species in the total catch in each sampling effort. An Index of Relative Importance (IRI) and Shannon diversity index (H') were used to evaluate relative abundance and species diversity of fishes, respectively. IRI is a measure of the relative abundance or commonness of the species based on number and weight of individuals in catches, as well as their frequency of occurrence (Kolding, 1989, 1999). IRI gives a better representation of the ecological importance of species rather than the weight, numbers or frequency of occurrence alone (Sanyanga, 1996).
Index of relative importance (% IRI) was calculated by the following formula:
IRI = X 100
Where % Wi and %Ni are percentage weight and number of each species of total catch, respectively. % Fi is percentage frequency of occurrence of each species in total number of settings. % Wj and % Nj are percentage weight and number of total species in total catch. % Fj is percentage frequency occurrence of total species in total number of setting. S is total number of species.
4.4Shannon index of diversity (H')
The Shannon index of diversity is a measure of the number of species weighted by their relative abundance (Begon et al., 1990). Shannon index of diversity (H’) was calculated using the formula:
H' = the Shannon diversity index
Pi = fraction of the entire population made up of species i
S = numbers of species encountered
∑ = sum from species 1 to species S
Shannon’s diversity index (H') was used to indicate diversity at different sampling sites and/or rivers. A high value indicates high species diversity.
The relationship between total length and total weight of the most dominant fish species was computed using power function as in Bagenal and Tesch (1978) as follows:
TW= a X TLb
TW= Total weight (gm)
TL= Total length (cm)
a = Intercept of the regression line
b = Slope of the regression line
4.6Condition factor (Fulton factor)
The well-being or plumpness of each dominant species was calculated as total weight in percent of total length cube (Lecren, 1951; Bagenal and Tesch, 1978). Fulton Condition Factor (%) was calculated as:
FCF = X 100
FCF = Fulton condition factor
TW = total weight in grams
TL = total length in cm
The ratio between the number of female and male. Sex ratio was determined using the formula:
Fecundity was determined gravimetrically method (MacGregor, 1957), by weighing all the eggs from each of the ovaries of gravid fish species (gonad maturity stage IV). Three sub-samples of 1 gm eggs were taken from different parts of ovary and counted and the average was calculated. The total number of eggs per ovary was calculated by extrapolation from the mean calculated. The relative fecundity was calculated by dividing the total number of eggs per fish weight. The relationship of fecundity with total length, total weight and ovary weight was determined. Fecundity was determined by the following formula.
F = aTLb
F = aTWb
F = aGwb
TL-Total length (cm)
TW-Total weight (g)
GW-Gonad weight (g)
Table 3: Macroscopic description of various gonadal stages, (Nikolsky, 1963)
IImmature, virgin-A pair of small thread-like, colourless organs (with slightly serrated edges, in C. gariepinus). Difficult to distinguish between the sexes (except in C. gariepinus).
Immature virgin-A pair of small, thread-like colourless organ. Difficult to distinguish between the sexes in B. tsanensis and O. niloticus. In C. gariepinus (size >18 cm) the ovary is discernible as tiny, bulb-like and pinkish in colour.
IIDeveloping virgin or recovering spent-Long thin, up to 1/2 length of body cavity but distinct opaque white in B. tsanensis and O. niloticus and translucent white in C. gariepinus, with distinct serrated edges and shorter.Developing virgin or recovering spent- Long thin, up to 1/2 length of body cavity thicker than the testis and translucent yellowish-white in B. tsanensis and O. niloticus and pink in C. gariepinus. Recovering spent has larger gonad size and athicker wall.
IIIMaturing or ripening-Long and thicker, 2/3 body cavity (or 1/2 in C. gariepinus), firm and more solid. Colour white in B. tsanensis, cream or beige in O. niloticus and greyish-white in C. gariepinus.Maturing or ripening-Long and thicker, 2/3 body cavity Colour yellowish in all. Ova discernible in all.
IVRipe and Running-Large thick and slimy. Milky white in B. tsanensis, creamy in O. niloticus and white in C. gariepinus. Sperm easily flows when pressed or cut. C. gariepinus testis has smoother edge.Ripe and running-Ovary large, yellow, almost filling the peritoneal cavity in all. Ova well developed and large may flow out when pressed.
VSpent-testis shrunk and flaccid. Numerous folds appear in O. niloticus, and serrated edges revert to original sharpness and colour changes grey in C. gariepinusSpent-Ovary shrunk and flaccid. Some remnants of disintegrating, opaque and ripe eggs appear in ovary of O. niloticus and sometimes in B. tsanensis; rarely in C. gariepinus. Colour changes translucent in O. niloticus and B. tsanensis but in C. gariepinus the ovary changes colour to greyish-red.
Description of gonads
Data collected were collated and analyzed using descriptive statistic (mean, standard error and percentage). Statistical comparison of data between and within zones was carried out using SPSS Version 16, analysis of variance (ANOVA), Mann-Whitney U test and line graphs using Origin 6 and excel statistical package (2007). Sex ratio of the fish was studied using Chi-square test (χ2) and values were tested using 95% confidence level. Correlation analysis was used ascertain the significance of these relationships. The exponents (b) of length weight relation were tested for departure from isometry (b=3) using t- statistics
4.10 Species description
The morphometric data have been converted into percentages with respect to standard length and head length. Standard univariate statistics methods (mean, standard deviation, maximum and minimum) have been used to summarize the morph metric and meristic data.
Chapter - 5
Results and Discussion
5.1A biotic parameters
A biotic factor land organisms, aquatic populations are also highly dependent upon the characteristics of the aquatic habitat, which support all their biological functions (reproduction, growth, feeding and sexual maturation). Thus, factors are the controlling factors for the aquatic life, since they shape most the biological functions of aquatic life (Murdoch and Martha, 1999). Cyprinids species as they lack parental care, fast flowing, clear and highly oxygenated water, and gravel-bed streams or rivers are generally their spawning ground requirements (Rodriguez-Ruiz and Granado Lorencio, 1992; Baras et al.,1996; Baras, 1997), due to their critical important in the development of eggs and larvae (Tomasson et al., 1984). Deposition of eggs in the gravel or pebble beds protect them from being washed away by riffle, and clear water will not cover them with affirm of obstructing the diffusion of oxygen (Lowe-McConnell, 1975).
Environmental factors such as temperature, vertical transparency (Secchi dept), pH, conductivity and TDS were compared among sampling sites (Table 4). Physical and chemical parameters were analyzed using nonparametric test (Mann-Whitney U). There was no significant difference (P>0.05) in pH, temperature, transparency, conductivity and TDS among all sampling sites (Table 4). However, there was significant difference between dry and wet seasons in pH, conductivity, transparency, TDS and temperature in all the sampling sites (P<0.001) (Appendix 10.1).
Table 4: A biotic parameters in the sampling sites with their Means ±SE in both dry and wet seasons (Mann-Whitney U test)
Physico-chemical Site Mean ± SE Sig.
Note: ns (P<0.05), (Average = Mean of mean)
5.2Fish species composition in the upper part of Blue Nile River
A total of eight fish species were identified during the present study in the upper part of the Blue Nile River below the fall. These were Labeobarbus intermedius, Labeobarbus nedgia, Labeobarbus crassibarbis, Labeo forskalii, Mormyrus kannume, Bagrus docmak, Clarias gariepinus and Oreochromis niloticus. These fishes representing by a single class Actinopterygii (ray-finned fishes), four orders, and five families (Table 5). The Cyprinidae were the dominant families. The freshwater fish fauna of upper part of Blue Nile River contains a mixture of Nilo-Sudanic (e.g., M. kannume, B. docmak and L. forskalii) and highland East African (e.g., L. intermedius, L. nedgia, L. crassibarbis, C. gariepinus and O. niloticus). L. intermedius, L. nedgia, L. crassibarbis, L. forskalii, B. docmak and M. kannume were present in all the sampling sites (Table 6). However, C. gariepinus was found in Sefania and Abenaze sampling sites but O. niloticus was found only in Sefania site.
Table 5: Fish species composition and local name in Amharic according to the local people
Species name local name family order
L. intermedius Nech Assa Cyprinidae Cypriniformes
L. forskalii Tubemate » » » »
L. crassibarbis Source » » » »
L. nedgia Mota » » » »
M. kannume Aishe Mormyridae Osteoglossiformes
B. docmak Fergus Bagridae Siluriformes
C. gariepinus Ambaza Clariidae » »
O. niloticus Koroso Cichlidae Perciformes
Table 6: Fish species presence in sampling sites (present, +, absent, -)
The fish species composition in upper part of the Blue Nile River during the study period was low as compared to results obtained by other workers in the Blue Nile and Tekeze drainage basins. Mohammed Omer (2010), reported 17 species from head of Blue Nile River (Lake Tana to Tisisat fall), Genanaw Tesfaye (2006), 10 species identified from Sanja, and Angereb Rivers, Moges Beletew (2007) 17 species from Beshilo, Dura and Ardi Rivers, Zeleke Berie (2007) 23 species from Beles and Gelegel Beles, Dereje Tewabe (2008) 27 species in Guang, Ayima, Gondwana and Shinfa Rivers, Tesfaye Melak (2009) 59 species from Baro and Tekeze Basins. Flow variability has an effect on fish assemblage, sometimes-high flows for instance can destroy fish habitat and can wash the eggs of the fish that have been already laid. On the other hand, during the dry season when the flow is low and when the water is reduced, the fishes are trapped in very small shallow pools that cause stress on fish and make very visible.
Below the Tisisat fall of Blue Nile River, fish species compositions were different from head of Blue Nile River and Lake Tana fish species composition as compared Mohammed Omer (2010) and (Nagekerke, 1997) works, respectively (Table 7). These result due to high waterfalls (40 m) at Tissisat ('smoking waters'), 30 km downstream from the Blue Nile outflow, effectively isolate the lake’s ichthyofauna from the lower Nile basin (de Graaf, 2003). In the present study L. forskalii, M. kannume and B. docmak were identified which were not recorded from de Graaf (2003) in Lake Tana and Mohammed Omer (2010) in head of Blue Nile River (Table 7). Labeobarbus nedgia and L. crassibarbis previously were reported only in Lake Tana (de Graaf, 2003). Mohammed Omer (2010) also identified these species from the head of Blue Nile River and Dereje Tewabe (2007) reported from Gondwana, Guang and Shinfa Rivers. Moreover, Dereje Tewabe et al. (2008) reported from survey of Tekeze hydropower dam and in the present study of the Blue Nile River below Tisisat fall. There was preliminary survey done by Golubtsov and Mina (2003), about 4-5km downstream from Tis issat falls that recorded four typical Nilotic species: Morymurs hasslequistii, Labeo forskalii, Raiamas senegalensis and Bagrus docmak. There was species composition variation between the present study and Golub tsov and Mina (2003), reported. Golubtsov and Mina (2003) recorded M. hasslequistii and R. senegalensis fish species but it was not found in the present study. M. kannume was recorded in the present study but Golubtsov and Mina (2003) did not record it. There might be variation in sampling habitats, fishing effort, type of gear they used and gill net efficiency, sampling seasons and altitude difference that contributed the variation in the catches.
Table 7: Fishes specie composition compression above and below the Blue Nile Fall (+, present and -, absent)
List of Species Lake Tana head of Blue Nile below the fall
L. trust forms+--
(Nagelkerke, 1997) (Mohammed Omer, 2010 (Present study, 2011)
5.2.1Diagnostic and descriptive characteristics of fishes
Labeobarbus intermedius (Banister, 1973) (Fig 4)
Diagnosis: It has variable body shape and heads, has characteristics of most L. intermedius species.
Description: It has variable body shape and head, has characteristics of most Labeobarbus species. Head naked, variable in dorsal profile. Mouth is terminal and protractile. Its HL 17.5-15.43% in SL. Depth of the body is little greater than head length; its depth 25.68-27.43% SL. It has medium eye 24.87-26.55% in HL. Its DFL and AFL are 20.61- 27.38% and 15.48-22.57% of SL respectively. Lip development is variable. Lower lip is interrupted and sometime continuous. Have two barbells on each side of the head. Its caudal peduncle length is greater than depth.
Coloration: Olive above yellow or pinkish beneath fins first brown or olive.
Distribution: The species is widely distributed in Ethiopian freshwater for example in Gibe, Megech, Sanja and Angereb, Borkena and Mille Rivers.
Fig 4: Lateral view of Labeobarbus intermedius
Labeobarbus crassibarbis (Nagelkerke & Sibbing, 1997) (Fig. 5)
Diagnosis: It has irregular dorsal, head profile.
Description: Body depth is greater than head length (its depth 15.30-49.05% SL). It has small eye (its diameter, 14.71-19.77). Its snout length and interorbital width is 27.45-35.44 and 27.45-35.46% in HL respectively.
Coloration: Mostly silver white beneath, the fins are whitish; but it differs depending on the habitat.
Distribution: It was reported from Tekeze River by Genanaw Tesfaye (2006) and Dereje Tewab (2008) and Lake Tana. (de Graaf, 2003).
Fig 5: Lateral view of Labeobarbus crassibarbis
Labeobarbus nedgia (Ruppell, 1836) (Fig. 6)
Diagnosis: Lips strongly developed both upper and lower, produced into a rounded or sub triangular lobes. It has fleshy rounded lobe on upper lip that curls back over the snout.
Description: Depth of the body is little greater than length of head (its depth 21.08-22.76% in SL). Its eye diameter is 22.5-32.36% in HL. Caudal peduncle length is grater than its depth (31.34-31.74% in SL).
Coloration: Fins olive or greenish above yellow beneath fins
Distribution: It was reported from Lake Tana, Angereb, Sanja, Omo, Dedessa, Beles, Gelegel Beles and Borkena Rivers.
Fig 6: Lateral view of Labeobarbus nedgia
Clarias gariepinus (Burchell, 1822) (Fig. 7)
Diagnosis: It has no adipose fin and scales in caudal peduncles and lateral line.
Description: depth of the body is less than length of the head (its depth 8-12.95 in % SL). The upper surface of head more or less distinctly granulate; occipital process angular. Its Eye is very small, its diameter of 4.44-6.02% in HL. It has wide interorbital width (30-31.91% in HL). Mouth is terminal and large Pectoral spin.
Coloration: Dark, grayish-black above and creamy-white underside.
Distribution: All Ethiopian freshwater.
Fig 7: Lateral view of Clarias gariepinus
Mormyrus Kannume (Forsskål, 1775) (Fig. 8)
Diagnosis: Snout at least nearly as long as postorbital part of head; dorsal in advance of base of ventral fins with rays; anal rays; scale in lateral line.
Description: Depth of the body is less than length of head (its depth 20.71-23.41% in SL). Upper profile of head is descending in straight line. It has small eye (14.4 -19.67% in HL). Paired and vertical fins all present; narrow caudal peduncle depth (6.82-9.39% SL) and deeply forked caudal fin. Dorsal fin rays 51-59, Anal fin rays 22-23. Dorsal and anal fins are opposite each other on the posterior part of body.
Coloration: Brownish or olive above and white in beneath.
Distribution: Gendewuha, Guang, Omo, Angereb, Ayima and Gibe Rivers.
Fig 8: Lateral view of Mormyrus kannume
Bagrus docmak (Forskalii, 1775) (Fig. 9).
Diagnosis: Body is slightly elongated. It has long barbells.
Description: Depth of the body is almost equal to head length (18.9-26.33% SL). Its head much depressed and smooth above. It has short snout length (7.94-10.61% in HL). It has relatively small eye (10-14.22% HL). Barbell length is much greater than head length. Caudal peduncle length is greater than its depth. Caudal is deeply forked.
Coloration: Grayish blue to dark olive above, white beneath.
Distribution: Guang, Omo, Sanja, Angereb, Ayima, Beles and Gelegel Beles Rivers.
Fig 9: Lateral view of Bagrus docmak
Labeo forskalii (Rüppell, 1835) (Fig. 10)
Diagnosis: Labial folds well-developed sucker around the mouth distinguishes this species, rostral flap large and horny tubercles on the snout.
Description: Body more or less compressed, its depth 19.02- 20.99%in SL. Snout is swollen with distinct curved transverse groove above. Snout length is greater than head length (its length 41.12 – 54.55%in HL). It has 11 to 12 dorsal fin rays and 18 to 21 caudal fin rays.
Coloration: Dark olive above and on the sides, whet beneath.
Distribution: Dubus, Angereb, Sanja, Tekeze, Baro, Omo, Gendewuha, Guang, Ayima and Gibe, Beles and Gelgel Beles Rivers.
Fig 10: Lateral view of Labeo forskalii
Oreochromis niloticus (Linnaeus, 1758) (Fig. 11)
Diagnosis: The most distinguishing characteristic of O. niloticus species is the presence of regular vertical stripes throughout the depth of caudal fin.
Description: Depth of the body is greater than the length of head (its depth 34.97-43.56% SL). Snout rounded, with straight or slightly convex upper profile. It has relative large eye, its diameter 16.37-24.07% in HL. The pectoral and pelvic fin length is 28-34.25 and 21.33-25.56% SL respectively.
Coloration: Brown or grey to dark olive color.
Distribution: Almost all Ethiopian freshwater.
Fig 11: Lateral view of Oreochromis niloticus
5.2.2Species diversity and abundance
Labeobarbus intermedius, L. nedgia and L. forskalii were common in all the sampling sites in both seasons. However, M. kannume and B. docmak were found in all the sampling sites during wet season but it was absent during dry season at Wm site (Table 9). Clarias gariepinus was found both in Se and Ab sites during the dry and wet seasons but absent in Wm site at both sampling periods. Oreochromis niloticus did not found in both Ab and Wm sites during the dry and wet seasons. The number of fish species is higher at Se sampling site and lower in Wm sampling site (Table 9). Eight species at Se and six species from Wm sampling sites were recorded (Table 8). Blue Nile River below the Blue Nile Fall was dominated by the Family Cyprinidae and mainly by the genus Labeobarbus.
Table 8: Fish distribution among the sampling sites both dry and wet seasons (+: present;- :absent)
Se Ab Wm
Fish species family dry wet dry wet dry wet
Shannon diversity index (H') was used to evaluate species diversity of sampling sites. Shannon diversity index explains both variety and the relative abundance of fish species (Naesje et al., 2004). The species diversity in Se site showed more diversity than Abenaze and Wotetomider in dry season but it is the lowest in wet seasons (Table 9 &10 and Fig 14). The H' was higher in Se sampling site with the values of (H' = 1.44) followed by Ab (H'= 1.33) and Wm (H' = 1.23) in dry season sampling period (Table 9). However, the H' was higher in Wm sampling site with the values of (H' = 1.62) followed by Ab (H' = 1.60) and Se (H’ = 1.58) in wet season sampling period (Table 10).
Table 9: Shannon diversity index (H') and number (N) of fish species in dry season
H'/N Sampling sites
Se Ab Wm
Table 10: Shannon diversity index and number of fish species in wet season
H'/N Sampling sites
Se Ab Wm
Fig 12: Shannon diversity index (H') and Number of fish species in both dry and wet seasons
During the study period, 128 kg and 232 kg total biomass of specimens were collected during wet and dry seasons, respectively (Table 11). The number of fish species was higher in dry season than wet season. However, Shannon diversity index (H') value was higher in wet season in all the sampling sites (Fig 12).
Table 11: Number and total biomass (kg) of fish during wet and dry season
Season Total weight (kg) Total number
Dry 232 553
Wet 128 304
Dry season showed higher values than wet season in terms of weight (kg) and number of specimens of fishes. The reason would probably be during wet seasons there is high turbidity of river, speedy run-off, and low temperature that attributed less number of fish catch in wet season. During wet season, there is also higher water discharge; fishes could be highly dispersed in the large volume of water than dry season and it becomes difficult to catch them. In addition to the variation in catches between wet and dry seasons might be variation gill net efficiency and time of setting of gill net might also contribute to variation in the catches. The efficiency of gill nets could be decreased by logs, leaves, roots that were brought by flooding.
188.8.131.52Relative abundance of fish during wet and dry seasons
The species composition of gillnet and monofilament catches both in dry and wet season ranked based on the IRI value for different sampling site (Table 12 and 13). Labeobarbus intermedius was the most abundant species during the study period and constituting of 39.67% in the total number of catch. L. forskalii and M. kannume were found in relative abundance of 27.77% and 11.67% respectively (Table 12). The other species, L. nedgia, B. docmak, L. crassibarbis, C. gariepinus and O. niloticus were found in 9.59%, 5.13%, 3.5%, 1.98% and 0.70%, respectively.
There was significant difference in fish specimen abundance between dry and wet season except L. crassibarbis, B. docmak and C. gariepinus (Table 12). Labeobarbus intermedius was the most important fish species in both dry and wet season in all sites (Table 12 and 13). Labeo forskalii was very important in all sampling site except Wm during the wet season. Mormyrus kannume was important in all sites except in Wm in wet season but was less important in all sites during dry season.
Labeobarbus intermedius and L. forskalii showed very highly significant variation in number of catch between dry and wet season (P<0.001). Mormyrus kannume and L. nedgia showed significant variation in number of catch between dry and wet season (P<0.01) and (P< 0.05) respectively (Table 12). However, B. docmak, C. gariepinus, L. crassibarbis and O. niloticus did not show significant variation in number of catch between dry and wet season (P>0.05).
Table 12: Species number and percentage composition of both in dry and wet season in sampling sites (One way ANOVA)
Fish species dry wet total percentage composition sig.
L. intermedius 243 97 340 39.67 0.000***
L. forskalii 179 59 238 27.77 0.000 ***
L. nedgia 52 30 82 9.57 0.015*
L. crassibarbis 14 16 30 3.50 0.715 ns
M. kannume 31 69 100 11.67 0.00 **
B. docmak 17 27 44 5.13 0.132 ns
C. gariepinus 11 6 17 1.98 0.225 ns
O. niloticus 6 0 6 0.70-
Note: *(P<0.05) (significant), **(P<0.01) (highly significant), ***(P<0.001) (very highly significant), and ns (P>0.05) (non-significant)
The species collected were analyzed based on the Index of Relative Importance. Accordingly, L. intermedius % IRI values (58.82%, 54.54%, and 48.05%) and (30.55%, 42.17%, 43.58%) in Se, Ab and Wm during wet and dry seasons respectively given in Table (13and 14). The percentage IRI of L. forskalii in dry season was (24.56%, 37.27% and 22.41%) in Se, Ab and Wm, respectively. The percentage IRI value of L. forskalii was higher both in dry and wet season in all the sampling sites (Table 13 and 14). The % IRI value of M. kannume was higher in Se and Ab sites during wet season. Nevertheless, it had small % IRI value in Wm site during wet season and in all sampling sites during dry season (Table 13 and 14). During dry season L. intermedius, L. forskalii and L. nedgia were the most important species with in Se and Wm sampling sites whereas in Ab site the most important species were L. intermedius, L. forskalii and M. kannume. Percentage IRI value from the pooled catch in sampling sites for L. intermedius (51.92%), L. forskalii (29.14%), L. nedgia (6.81%) and M. kannume (5.99%) were in order of their decreasing importance (Table 15).
Table 13: Percentage index of relative importance of fish species in dry season
Table 14: Percentage index of relative importance of fish species during wet season
Percentage IRI of L. intermedius was higher at Se and lower at Wm in dry season and it was higher at Wm and lower at Se site in wet season. Percentage of IRI of L. forskalii was higher at Ab and lower at Wm in dry season and it was higher at Se and lower at Wm (Table 13 and Fig 13). Percentage IRI of M. kannume was higher during wet season and lower during dry season in all sampling sites.
Fig 13: Percentage IRI of dominant fish species in sampling sites during dry and wet season
There might be several reasons for changes in abundance between wet and dry seasons. Variation in available nutrients and habitats, fishing effort, fish behavior, size and life history stages of fishes might all contribute to variation in abundance of the catches. Moreover, water level (Karenge and Kolding, 1995) and turbidity of water may also affect abundance.
Table 15: Pooled catch of IRI and H' values in both dry and wet seasons at all the sampling sites
Total857- 359916.6 - - -3887.01
184.108.40.206Length frequency distribution of the dominate fish species
The length frequency distribution of the most dominant species of L. intermedius, L. forskalii and M. kannume are showed in (Figure 14). Labeobarbus intermedius the most dominant species had total length rage from 17 to 52.3 cm, with the mean and standard error of total length was 32.5±0.50 (Fig 14). Labeo forskalii is the second most abundant species with total length range from 13.8 to 46.5 cm with mean and standard error of 34.3 ±0.39 (Fig 14). Mormyrus kannume is the third abundant species had total length rage from 25.2 to 40.8 cm with mean and standard error of 32.2± 0.44 (Fig 14).
Fig 14: Length frequency distribution of L. intermedius (N= 340), L. forskalii (N=238) and M. kannume (N= 100) respectively
5.3Some biological aspects of the dominant fish species
The relationship between total length and total weight for most dominant species of L. intermedius, L. forskalii and M. kannume were curvilinear and showed significant variation (P<0.001).
In fishes, the regression coefficient b=3 describes isometric growth, when the value becomes exactly 3, if the fishes retain the same shape and their specific gravity remains unchanged during their life time (Ricker, 1975). If the weight increased according to the fish length, it is said to be isometric growth (Mansor Mat Isa S.A.S.A., 2001). However, fishes may have “b” value greater or less than 3, a condition of allometric growth (Bagenal and Tesch, 1978). A value less than 3.0 shows that the fish becomes lighter (-ve allometric) or greater than 3.0 indicates that the fish become heavier (+ve allometric) for a particular length as it increases in size (Wootton, 1998; Zafar et al., 2003). L. intermedius in the upper part of Blue Nile River showed nearly isometric growth, which means the weight of these fishes increases as the cub of length because the b value is nearly 3 for these fish species in river (Fig 15). This value was close to the values reported for some freshwater fish species by Genanew Tesfaye (2006), in Angereb and Sanja Rivers, Wassie Anteneh (2005), in Dirma and Megech Rivers, Abebe Getahun et al., (2008) in Rib River, Assefa Tessema (2010), in Borkena and Mille Rivers and Mohammed Omer (2010), in head of Blue Nile River. On the other hand the b values obtained in this study area for L. forskalii and M. kannume show negative allometric growth unlike that reported by Dereje Tewabe (2006) in Gendewuha, Guang, Shinfa and Ayima Rivers and Genanaw Tesfaye (2006), in River Angreb. However, the result obtained in this study b value for L. forskalii in upper part of Blue Nile River is in agreement with the values obtained by Zeleke Berie (2009) from Gelegel Beles River.
Fig 15: Length-weight relationship of L. intermedius, L. forskalii and M. kannume respectively
5.3.2Fulton’s condition factor (FCF)
The mean Fulton condition factor value obtained in the present study for L. intermedius in the Blue Nile River below the Tisisat fall was 0.99, which was less than reported by Genanaw Tesfaye (2006), from Angereb and Sanja Rivers with a value of 1.06, Dereje Tewabe (2008), from Gondwana, Guang and Shinfa Rivers with a value of 1.12, Assefa Tessema (2010), with a values of 1.23 and 1.31 in Borkena and Mille Rivers. Nevertheless, it is higher than the result obtained by Mohammed Omer (2010), with value of 0.87 in a head of Blue Nile River. The present FCF value of L. intermedius was similar to that reported by Zeleke Berie (2009), in Gelegel Beles River. The measurement of fish condition can be linked to the general health, fat and lipid content prey or food availability, reproductive potential, environmental condition and water level fluctuation. In general, higher condition is associated with higher energy (fat) content, increasing food base, reproduction potential or more favorable environmental condition (Pauker and Cottle, 2004).
Table 16: Mean and Standard deviation of Fulton condition factor both by sex and season: P= significance difference (Mann-Whitney U test) between sex and seasons of dominant fish species
Fish Sex Mean ± SD P Season Mean ± SD P
Note: ** =P<0.01, ns =P>0.05, (Average =Mean of mean)
The mean Fulton condition factor of L. intermedius did not show significant variation in sex and season respectively (Table 16). The mean Fulton condition factors of L. forskalii in dry season was (0.85±0.12) which is higher than wet season (0.80±0.06). There was significant variation in Fulton condition factor of L. forskalii between dry and wet season (P<0.01), but it did not showed significant variation between sexes (Table 16). This result is in agreement with Genanaw Tesfaye (2006) that reported significant variation (P<0.05) for L. forskalii between dry and wet seasons in Sanja and Angereb Rivers. Labeo forskalii was in better condition in dry season than in wet season. The mean Fulton condition factor of M. kannume was (1.49±0.05) and (1.32±0.047) in sex and season, respectively. There was no significant variation between Fulton condition factor by sex and seasons. The low Fulton condition factor of fishes of the river is probably because of fluctuation in factors such as food quantity and quality, water level and flow rate and temperature.
5.3.3Some aspect of reproductive biology
From total number of 857 specimens of fish collected from upper part of Blue Nile River during the study period, 17 (1.98%) specimens were unsexed, hence excluded from sex ratio study. Totally 840 (98.02%) specimens were sexed of which 619 (73.69%) were females and 221 (26.31%) were males. In general, females were numerous than males. The chi-square test showed that there were significant variations between number of male and female fish species of L. intermedius, L. forskalii, L. crassibarbis and B. docmak (Table 18). The sex ratio of L. intermedius, L. forskalii and L. crassibarbis showed significant variation (χ², P<0.001). B. docmak showed significant variation (χ², P<0.01) between number of male and female (Table 18). However, L. nedgia, M. kannume, C. gariepinus and O. niloticus did not show significant variation between male and female. During the study period, the highest deviation in sex ratios was observed in L. crassibarbis (6.50:1) and the second one was O. niloticus (5:1) (Table17).
Table 1: Number of males, females and the corresponding sex ratios (pooled from all sites) (One way ANOVA)
Species F M Sex ratio χ² P (F: M)
Note: **highly significance (P<0.01), *** Very highly significance (P<0.001), (ns) not significant (P>0.05)
The imbalance of female to male ratio was most probably related to different biological mechanisms such as differential maturity rates, differential mortality rates and differential migratory rates between the male and female sexes (Sandovy and Shapiro, 1987; Matsuyama et at., 1988).
Absolute fecundities of the most dominant fish species (L. intermedius) was determined based on number of eggs per total length, total body weight and gonad weight. Eleven specimens of L. intermedius with total length ranging from 25.5 to 47.4 cm, mean and standard error of 38.7 and 2.35 had mean absolute fecundity (AF) of 3705 and ranged from 1345 to 7235 eggs. The relationship between AF with TL, TW and Gonad Weight of L. intermedius was linear. In general, absolute fecundity of L. intermedius was strongly positive correlated with TL. TW and GW (Fig 16).
The information about fecundity of large Barbus fish species in Africa is scarce (Marshall, 1995). There was few data on the fecundity of Ethiopian large Barbus. Alekseyev et al. (1996) and Wassie Anteneh (2005) studied fecundity of large Barbus in Lake Tana and its tributaries. The absolute fecundity of L. bervicephalus and L. truttiformis ranged from 1284 to 4563 and 1732 to 8134 eggs, respectively in Lake Tana (Wassie Anteneh, 2005). Compared to Lake Tana Labeobarbus species a similar sized female L. intermedius in the Blue Nile River below the Tisisat fall have more or less similar number. The absolute fecundity of L. intermedius reported by Dereje Tewabe (2008) ranged from 542 to 13769 in Gendewuha, Guang, Shinfa and Ayima Rivers. In Borkena and Mille Rivers reported the absolute fecundity of L. intermedius ranged from 2736-12124 (Assefa Tessma, 2010).
Fig 16: ABC Absolute fecundity with total length, total weight and Gonad weight relation in L. intermedius (n= 11)
Chapter - 6
Fishing Activity and Its Problems in the Study Area
Questionnaires were developed and interviewed the local inhabitant of villages near the River: Sefania, Abenaze and Wotetomider to know the fishing activity of the farmers and identify major problems. The information obtained from the questionnaires and from personal communication was used to state about the fishing activity in the river and identify its problems.
There were 30 farmers in the study area that were selected and interviewed. The farmers’ source of income is crop and animal farming. Fishery was an additional source of food. They fish for their own consumption and as a gift for relatives. The entire farmers in upper part of Blue Nile River were seasonal and the fishing activity takes place only from the river. They usually start fishing activities in the river in the middle of November. They start during this time because in most cases the water level starts to lower.
The fish catch data from upper part of the Blue Nile River was not available. The farmers fishing activity takes place at night. However, rough estimates can be made from the observations I had and interviews made with the farmers. Accordingly, fishing activity takes place at about three sites along the stretch of the river. It takes place for about six months (15 November to end of May) sometimes in June and July. Farmers catches fish on average four day per week and 17 days per month. They estimated their daily catch up on average five fish/night/person (about 10 kg/night/person). From each site 204kg of fish harvest per six months per person per site. In all sampling site an average of 18.36 quintals of fish has been harvest annually from the three sampling site. The method I used to estimate based on interview result. Fishing intensity in the study area was higher starting from January to May (Fig 17). Fish potential of the river is decline from time to time due to environmental fluctuation (personal communication). According to Gebru Asrat (personal communication), few species extinct from the river for example, L. horie in local language “Assam nalbari”. This fish was present in the river few years ago and they were catch frequently but now it does not found. The probable reason they put was fluctuation of the river volume year-to-year and other environmental variations. For example, in 2010 the river was total blocked at the source in Lake Tana, during this time there was numerous fish massive fish death and also catch by the local people using hand. In addition, huge amount of fish was dead on October (2010) after heavy ran fall. The reason of this the rainfall is mixe up with snow. This leads to increase the coldness of the river.
Fig 17: Farmers fishing time in the study area
There is no as such any technical assistance (extension service) for the local community with regard to utilization and management of the fish resource. There is no any modern fishing gear in the area. Most local fishermen use hook and line (Local name is mekatin) and Castnet (Local name is mereab) for catching fish. The hook and line has got three size categories (Large, medium and small). Those local fishermen used part of the flesh of fish as bait. Some of the local fishermen used locally made gill nets with mesh size of approximately 12cm.
When the volume of the river is becoming low there is high fishing intensity by local community and the fish prey by other aquatic animals such as birds and crocodiles. Most of the respondents are willing to cooperate in any measures that would lead to sustainable utilization of the fish resources. They are also eager to get modem fishing gear like gillnets.
Farmers identify some of the fish species with their local names: "Nech Assa" (L. intermedius), "Tubemate" (L. forskalii), "Source" (L. crassibarbis), "Mota" (L. nedgia), “Aishe” (M. kannume),”Fergus” (B. docmak), "Ambaza" (C. gariepinus), "Koroso" (O. niloticus, Nile tilapia). They very well understand that there is diversity of fish in upper head of Blue Nile River. Almost all of the respondents said that more than, 90% of the catch is composed of L. forskalii, M. kannume, L. intermedius, and B. docmak (this especially used after drying). Among the above fish, species the farmer prefer to consume L. intermedius and L. forskalii. They prefer the two species because they assume high quality and the fishes are attractive when seen externally. All of the respondents do not have storage facilities but they have tried to improve the shelf life of the fish by sun drying methods by making a strip of the flesh of catfish and Bagrus docmak
6.2Problems in fishing activities
Main problems mentioned by respondents in upper part of Blue Nile River were: Lack of proper fishing gears; almost all of them use hook and line and castnet for fishing, lack of knowledge in fishing and fish processing, lack of infrastructure and market, especially those local fisherman live far from woreda town, lack of post-harvest technology in case of excess production. As a result, the fishermen catch fish only for household consumption purposes. There is no extension service that assists the fishery activities.
Chapter - 7
Limitation of the Study
Data were collected only in two seasons due to logistic and budget constraints and hence it was difficult to collect enough information on reproductive biology of dominant fish species: L. intermedius, L. forskalii and M. kannume. In addition to this, sampling duration and sampling sites were limited due to budget and rugged topography location so that the chance of obtaining many new species in the rivers became low. The efficiency of fishing gears was also another limitation for my current study.
Chapter - 8
Conclusion and Recommandations
•Eight species of fishes included in 5 families and 4 orders were investigated from upper part of Blue Nile River.
•Diversity of the fish fauna of the River is dominated by cyprinid fish species. L. intermedius, L. forskalii and M. kannume were the most dominant fish species in number and total biomass during the study periods.
•Sefania site had higher fish diversity in dry season than the other sampling sites. But it had lower diversity in wet season as compared to Abenaze and Wotetomider. Shannon diversity value (H’) of Sefania was (1.44) in dry and (1.58)in wet season, where as Abenaze and Wotetomider had 1.33 and 1.23 in dry and 1.60 and 1.62 in wet season respectively.
•L. intermedius, L. forskalii and M. kannume were the most important fish species during wet season with IRI value of 46.64%, 17.69% and 16.87%, respectively. Whereas L. intermedius, L. forskalii and L. nedgia were the most dominant fish, species during dry season with IRI value of 57.32%, 28.96% and 8.27%, respectively.
•L. intermedius, L. forskalii and M. kannume were with highest diversity, with the Shannon diversity index value of 0.37, 0.36 and 0.25, respectively.
•L. intermedius, L. forskalii and M. kannume were the most important fish species in the upper part of the Blue Nile River. Their compositions from the total catches were 39.67%, 27.77% and 11.67% respectively.
•The length weight relationships for L. intermedius, L. forskalii and M. kannume were curvilinear. L. intermedius showed nearly isometric relation, but L. forskalii and M. kannume showed negative allometric relation.
•There was significant difference in Fulton condition factor for L. forskalii between dry and wet seasons (P<0.01).
•Fulton condition factor of L. forskalii in dry and wet seasons was (0.85±0.12) and (0.80±0.06), respectively. Therefore, L. forskalii was in better condition in dry season than wet season.
•The chi-square test analysis showed that there was significance variation in number of male and female of L. intermedius and L. forskalii with (P< 0.001). However, M. kannume did not showed significant variation in number of male and female.
•Fecundity was found to have linear relation with total length, total weight and gonad weight for L. intermedius.
• The upper part of Blue Nile River has a number of fish species and the people in this area have fish consuming habit.
•L. intermedius, L. forskalii, M. kannume and B. docmak are the most subsistence fish species in of Blue Nile River below the Tisisat fall.
•L. intermedius and L. forskalii are the most preferred fish species consumed by the local people.
Detailed studies and investigations are required on:
•The diversity, abundance and biology of fish species was carried out only in upper part of the River only in two seasons over relatively short period of time. Besides, the study was conducted only at three sites. For comprehensive assessment on the magnitude of fish, diversity in these river investigations should be conducted throughout the year using more sites and different sampling methods. Investigations should also be done along the river until the border of Sudan by selecting many more suitable sampling sites.
•Food and feeding behaviors of the fish species in the river.
•Ecological issues specially that of catchment area of the rivers. There are indications of severe degradations of the river basins particularly the upper part of the river catchment area. Major threats to the basins are related to deforestation and erosion. This issue requires scientific study so that sustainable utilization of the resources is designed.
•The water released from Lake Tana should be constant, so that it does not affect the natural flow of the regime.
•There is lack of information on the fish and fisheries in the river. This should be given emphasis by the respective institutions or organizations so as to introduce appropriate extension systems to identify and exploit the fishery resources in a sustainable manner.
•Fishermen need to be encouraged through training and provision of appropriate fishing gears, since crocodile problem for gillnet is paramount in the area. Organizing fishermen in cooperatives with strong extension network with expertise is recommended.
•The government should be implement fisheries legislation to encourage the fishermen
• Awareness creassion should be given for fishermen’s about fishing activity and supply appropriate fishing gears.
•Integrated watershed management should be done in the river drainage basins.
•Fish species of L. nedgia and L. crassibarbis were required further identification because of previously the two species are endemic to Lake Tana only.
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Physico chemical parameters of the river at sampling site both in dry and wet seasons
Note: ***(Very highly significant)
Morphometric and merstic measurements of Fishes
Morphometric and Merstic characteristics of L. intermedius
Morphometric and merstic characteristics of L. forskalii
Morphometric and merstic characteristics of L. nedgia
Morphometric and merstic characteristics of M. kannume
Morphometric and merstic characteristics of B. docmak
Morphometric and merstic character of L. crassibarbis
Morphometric and merstic characteristics of C. gariepinus
Morphometric and Merstic characteristics of O. niloticus
Name of respondent ___________
1.Age of respondent _________
5.Total number of family___________?
6.Income per month in ET. Birr _____________?
7.What is your Source of Income?
8.Do you engage fishing activity?
9.If your answer is yes for Q.7. Where do you fish?
10.When do you actively involved in fishing (within a day)?
11.When did you start fishing__________?
12.What type of fishing gear you use?
B.Hook and line
13.How much the mesh size you use for fishing__________?
14.What types of fish you fish? ____________
15.How many days do you fish per month____________?
16.How many kg of fish you catch per week__________?
17.Which type of fish you prefer to eat____________?
18.Which type of fish consumers prefer to buy__________?
19.When do you fish more fish within a year___________?
Which type of fish___________?
20.Do you use prevention methods of fish spoilage?
21.If your answer is yes, what type of prevention method you use__________?
22.How much the Price of each fish that you fish__________?
23.How is trend of the price?
24.How much is income generated from fishing_________?
25.What are the major changes occurred in fishery__________?
26.What are the major problems to stay in this business_________?
27.Do you know the type of fish that has become extinct in this area?
28.If your answer yes for Q.28 which type of fish are extinct?