Browsing by Author "Getahun, Abebe (PhD)"

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    Current status and trends of fishes and fishery of a shallow rift valley lake, Lake Ziway, Ethiopia
    (Addis Ababa University, 2016-06) Abera, Lemma; Getahun, Abebe (PhD)
    Lake Ziway is an economically important lake in the country. However, the physico-chemical parameters of the lake seem to be threatened by anthropogenic and climatic factors, which in turn affect biotic factors as reflected in fish catch. A study was made to assess the status and trends of fishes and fishery during October 2012 to September 2014 in Lake Ziway. Conductivity and pH showed more or less no change during the last two decades as the mean values ranged from 361.5±9.7 to 484.51±15.3 μS/cm and 8.03±0.2 to 8.37±0.1, respectively. Dissolved oxygen content has higher values around the northern part of the lake at the inlet of Meki River (5.71±0.6) and Ketar River (6.01±0.5). Ten fish species were identified with low species diversity for the lake (H′ value of 1.67). The composition of the fishes has undergone some changes as compared to the last few decades. For instance, Carassius auratus and Labeobarbus microterolepis were not cought in this study. Inaddition, Cyprinus carpio, which was never reported inearlier catch earlier, attained the highest relative frequency (25.19 %) in this study, next to Oreochromis niloticus (27.88 %), and then followed by Carassius carassius (20.71%) and Clarias gariepinus (20.51%). Canonical Correspondence Analysis (CCA) showed that the average abundance of C. carpio, ii C. carassius and C. gariepinus were positively correlated with nutrients, whereas the abundance of Labeobarbus ethiopicus and Labeobarbus intermedius had negative correlation with most of the physico-chemical variables. Some biometric measurements (length-weight relationship, condition factor, and sex ratio) were examined for the fishes. The length-weight relationship in Barbus paludinosus, C. carassius, C. carpio, L. intermedius, C. gariepinus, Tilapia zillii and O. niloticus were curvilinear and statistically highly significant (P < 0.05). Fulton Condition Factor values (mean ± SD) of the fishes were 1.26±0.19 (B. paludinosus), 1.52±0.14 (C. carpio), 2.13±0.57 (C. carassius), 1.73±0.38 (L. intermedius), 0.76±0.21 (C. gariepinus), 1.9±0.35 (T. zillii) and 1.83±0.21 (O. niloticus) for both sexes. Females were more numerous than males for all commercially important fish species except C. gariepinus, and the ratio was significantly different from the hypothetical distribution of 1:1 (X2 > 4). The frequency of ripe C.carpio as well as GSI values were generally high during February through to June and peaking between March and May sugesting that fish resources were intensivelly in breeding condition. Fecundity, for C. carpio of fork length from 32 cm to 46 cm, ranged from 75,645 and 356,743 eggs with a mean of 210,538. Fecundity was significantly (P < 0.05) related to fork length to total weight as well as to gonad weight. The relationship between fecundity and fork length was curvilinear whereas that between fecundity and total weight and that between fecundity and gonad weight were linear. The fish catch of Lake Ziway currently declined from 3180 tons in 1997 to 1157.14 tons in 2014. Most of the threats resulted from the anthropogenic impacts on the lake. Increased pressure in fishing was a problem in the lake. Currently, plenty of pumps are abstracting fresh iii water from the lake by state and private commercial farms throughout the year that are critically impacting the water level of Lake Ziway. As a result, the lake ecosystem is being affected by catchment degradation and siltation. The study suggested that if nutrient levels continue to increase and water levels continue to decline, further changes in fish composition can be expected in the lake, especially with a shift towards fish that are mainly turbiditytolerant species such as C. carpio. The study showed that the fishery sector has been of critical importance to the economy and to the social well-being of the fishermen in the study area. However, current harvest trends and fishery conditions put these attributes of the production at risk. It is threatened with problems of open access to the resources, pollutions, marketing, and lack of technology. Hence, appropriate management is an urgent requirement that could assist in sustainable exploitation of the resources, so that the resource could contribute to food security in the study area in particular and in the country in general
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    Diversity, Relative Abundance and Biology of Fishes in Angereb and Sanja Rivers, Tekeze Basin, Ethiopia
    (Addis Ababa University, 2006-06) Tesfaye, Genanaw; Getahun, Abebe (PhD)
    Diversity and relative abundance of fish species of Rivers Angereb and Sanja were studied from samples (923 specimens) collected during November 2004 to October 2005. The samples were collected in the dry season and wet season. Fish sampling was done using gill nets with various stretched mesh size, hooks and line, monofilament nets with different mesh size and cast nets. Ten fish species were identified from the two rivers and these are included in the families Cyprinidae, Cichlidae, Mormyridae, Clariidae and Bagridae. The fish species identified are East African and Nilo-Sudanic in forms. Cyprinid fish, L. forskalii, was the most dominant both in number and weight in both rivers during the two sampling seasons. Analysis of variance shows that there were significant variations both in number and weight of fish specimens between the two seasons. The three most dominant fish species in the rivers are L. forskalii, L. cf. intermedius and L. nedgia. The length-weight relationship for these species were found to be curvilinear and described by TW = 0.0715TL2.47, TW = 0.0269TL2.96 and TL = 0.0269TL2.74 respectively in Angereb River. It was TW = 0.01TL3.021, TW = 0.0057TL3.18 and TW = 0.006TL3.14 for L. forskalii, L. cf. intermedius and L. nedgia respectively in Sanja River. The mean FCF for L. forksalii, L.cf. intermedius and L. nedgia were 1.26, 1.14 and 1.18 in Angereb River and 1.09, 1.05 and 1.05 in Sanja River respectively. There was significant variation (ANOVA, P < 0.05) in mean FCF of L. forskalii and L. intermedius in the two rivers. In both rivers females were more numerous (Chi-square, P < 0.05) than males. The mean absolute fecundity of L. forskalii ranging in length from 21 to 25cm FL and mean body weight of 229 gm was 48120. The smallest count was 27094 eggs in fish with 14 gm total weight and 22.2 cm fork length. The highest was 120314 eggs in fish with 1023 gm total weight and 37 cm fork length. Fecundity of the species in the rivers was linear when related to total weight, fork length and gonad weight. Key words/phrases: Rivers, Angereb, Sanja, fish diversity, relative abundance, length-weight relationship, Fulton Condition Factor.
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    Effects of Niger Cake Inclusion in Fish Feed as a Major Protein Source on Cation Dynamics in Nile Tilapia-Lettuce Aquaponics System
    (Addis Ababa University, 2016-07) Aziz, Tiruken; Getahun, Abebe (PhD)
    In aquaponics system the survival of cultured organisms is exclusively dependent on dissolved ions generated by the fish wastes. In this system fish meal is mainly used as a major protein sources as a fish feed which is not affordable to developing countries despite its high cation compositions. Therefore, a study was conducted to investigate the cation dynamics in tilapia-lettuce aquaponics system by providing Niger cake in different proportions as replacement for fish meal in fish feed to compare its cation loading capacity with that of fish meal and a standard hydroponics. The experiment was done in five treatments with respect to the proportion of Niger cake; 0% (Control), 12.5% (TA), 25% (TB), 37.5% (TC), and 43% (TD) and each treatment in duplicates. One hydroponic treatment (H) was included in the experiment to check the performance of each treatment on cation dynamics with respect to lettuce. Water, fish and lettuce samples were collected from the system every week for cation analysis. Potassium was analyzed by Flame photometer; calcium using atomic absorption spectrophotometer and iron with spectrophotometer. The result of the experiment showed that higher Niger cake inclusion in the fish feed (43%), TD) resulted higher cation loading to the system than the control diet and less cation loading than the hydroponic solution. However, iron concentration in the aquaponics water showed significantly higher value than hydroponic solution (P>0.05). The lettuce cation content also showed that higher percentage of the alternative feed could provide higher concentration of calcium, iron and potassium than the control fish feed. Therefore, the higher percentage of alternative feed from plant sources such as Niger cake could provide higher cations for the cultured plants in an aquaponics system though these cations could not be comparable with the standard hydroponics. Key words Cation dynamics, Niger cake, Nile tilapia, Lettuce, Hydroponics, Aquaponics
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    The Effects of Stocking Density and Feed on the Growth Performance of Oreochromis Niloticus in Suspended Cage in Lake Babogaya, Ethiopia
    (Addis Ababa University, 2008-06) Mohammed, Kemal; Getahun, Abebe (PhD)
    The effects of stocking density and supplementary feeding on growth performance of Nile tilapia, O. niloticus in cage culture in Lake Babogaya were investigated for five months from February 2007 to July 2007. Juvenile of O. niloticus having a mean body weight of 30 gm and mean length of 12.5 cm were stocked in duplicates of five cages, with stocking densities of 50 (with and with out feed), 75, 100 and 125 per meter cube. The feed treatments were providing supplementary feeds with a composition of 60% sweeping meal, 20% crushed seed cotton and 20% pea flour, with a feeding rate of 2% of the body weight. The feed was divided equally into two and was fed twice a day. Growth change and feed conversion ratio of the stocked fish were studied for the sampling periods. The survival rates of the stocks were high in all treatments and were not affected by difference in stocking density. The results of this experiment indicated that significantly higher mean weight (MWT) and daily growth rate (DGR) were obtained from the lower stocking densities with feed (50 fish/m³), than those from the higher stocking densities (125 fish/m³) and the control stock (50 fish/m³) (P < 0.05). This result revealed that growth performance was negatively affected by stocking density. Moreover; feed had a strong positive effect on growth performance. The gut analysis result indicates the importance rank of natural feed (phytoplankton: Microcystis aeruginosa, Bacileariacaea and dinoflagellates) were 1st, 2nd and the 3rd respectively. The biodynamic of the Lake changed after April; dinoflagellates became more dominant and Microcystis aeruginosa became more decreased, but the importance rank remain the same throughout the sampling periods, which indicated O. niloticus is selective feeder and Microcystis aeruginosa, and Bacileariacaea are the preferred natural feed in Lake Babogaya. The least growth performance coincided with the decline of primary production, the change in biodynamic of the Lake and the vertical shifting of the natural feed to metalimnetic region. The negative growth of the control stock in May and June indicates that extensive cage culture practice is impossible while the primary production is decreasing and the natural feeds (phytoplankton and zooplankton) are shifted to the lower depth (metalimnetic region) from April to September unless the size of the cage is big enough to reach to the feed richer site of lower depth, but this has to take the DO concentration into consideration. A nematode parasite worm Contracaecum sp. with length of 2.6 to 4.5 cm and 5 to 7 in number per fish were identified in the gill cavity of the stocked fishes with size of 60 –100 g; however, frequent longer sized worms were not common in natural wild fishes of comparable size. But these parasites rarely occurred in bigger sized wild fish. The competition for feed of the wild fishes was very high which bring stress and competes for feed and space; during sampling and harvesting times between 17 – 89 % extra wild fishes were identified. Relatively improved growth was observed in those cages that were fixed toward shore side and in shallow water than the front lined cages that were hanged in deeper position which indicates the position of the cages has effect on growth performance. Key words / phrases: Cage culture, Lake Babogaya, stocking density
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    Fish Abundance and Socio-Economic Aspects of Lake Jipe Fisheries, Kenya/Tanzania Border
    (Addis Ababa Universty, 2004-07) Linus, Edward; Getahun, Abebe (PhD)
    Lake Jipe is a lake that is shared by two countries, Kenya and Tanzania, and is one of the water bodies where both human and natural activities have had great impacts both on the fish and fisheries. This study was aimed at identifying all the fish species found in the lake, detelmining the relative abundance of each of the species at selected sites and to assess the socio-economic aspects of fisheries in the lake. Fish sampling was done using gill nets of size 20 - 60 mm and fish identified to give a species inventory of the lake. Relative abundance was estimated using Catch Per Unit Effort (CPUE). A questionnaire was used to gather information on the socio-economic aspects. Nine species were identified from the lake. Catch Per Unit Effort (CPUE) showed that the introduced Oreochromis esclilelltlls was the most abundant in both seasons and also in all the sites, both in numbers and weights. Analysis of Yariance (ANOY A) indicated a significant difference in weight of specimens between the two seasons. The length-weight relationship for Bm·bus. Paludinosus, 0. esclIlentlts and O. jipe, which were the most common species in the lake, were found to be cnrvilinear. The mean seasonal Fulton condition factor was 2.0, 2.1, 1.3 and 0.9 for 0. jipe, 0. esculelltlls, B. paludilloSIlS and R. tangensis, respectively. There were no significant differences in the water parameters between the sampling sites, but there were significant differences for BOD, electrical conductivity and temperature between seasons. Gill nets were the most commonly used fishing gear by the local fishermen and a mesh size of 30mm was most pre felTed. Fish caught by the fishermen were both for commercial and subsistence purposes. Fish preservation methods included smoking and sun drying. This study realized that the challenges facing Lake Jipe are a complex mixture of socio-economic and ecological factors some of which include increased siltation, decreasing water quality and quantity, shrinking fishery, advancing water plants, agricultural expansion and expanding itTigation. KEYWORDS: Lake Jipe fisheries, Relative abundance, Socio-economic aspects, Kenya/Tanzania border
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    Spawning Migration and Reproductive Biology of Labeobarbus (Cyprinidae: Teleostei) of Lake Tana to Dirma and Megech Rivers, Ethiopia
    (Addis Ababa University, 2005-06) Anteneh, Wassie; Getahun, Abebe (PhD); Dejen, Eshete (PhD)
    The reproductive biology of the endemic ‘large’ Barbus (renamed Labeobarbus) species was studied from December 2003 to November 2004 in Dirma and Megech affluent rivers of Lake Tana. Fish and other environmental parameters were sampled monthly from November to June, bimonthly in July and weekly from August to October at the river mouths. Similarly, the spawning migration to upstream reaches of these rivers was monitored weekly in the peak breeding season (August to October) using 6, 8, 10, 12 stretched mesh size multi-filament and multi-mesh monofilament gillnets, fykes, local basket traps and hook-and-line fishing gears. Samples of fish caught were identified, measured, weighed, dissected and sexed. Changes in mean gonado-somatic index, Fulton’s condition factor and relative abundance of each particular Labeobarbus species were analyzed seasonally. Peak spawning generally occurred from August to October. Six species (L. brevicephalus, L. intermedius, L. megastoma, L. tsanensis, L. truttiformis and L. surkis) formed aggregation in the river mouths. The first species to congregate was L. megastoma, followed by L. tsanensis and L. truttiformis and the final were L. brevicephalus and L. surkis. Macrospatial segregation among these species between the two river mouths did not occur, however, except L. intermedius, temporal segregation was apparent in the river mouths in the spawning season. All these species, except L. surkis, that congregate in the river mouths ascend to upstream reaches of the rivers. This spawning run showed sequential patterns of segregation among the migrating Labeobarbus species. L. truttiformis and L. tsanensis were the first to migrate up rivers and L. megastoma just run next to them, however, L. brevicephalus was the last in the sequence of migration. Excluding the running (egg shedding) individuals, mean absolute fecundity and egg diameter of L. truttiformis, 4563 eggs and 1.99 mm, respectively, were higher than L. brevicephalus (2421 eggs and 1.97 mm) but their relative fecundity remained the same. The relationships of absolute fecundity with fork length, body weight, and gonad weight were curvilinear. Length-weight relationships were curvilinear and in agreement with the cube law. Based on the results obtained in this study and previous investigations in other affluent rivers, the Lake Tana Labeobarbus spawning strategies are hypothetically categorized into three: (1) obligate riverine spawners (L. brevicephalus, L. tsanensis, L.truttiformis), (2) generalists (spawning in the rivers and in Lake Tana) (L. acutirostris, L. intermedius, L. macrophtalmus, L. megastoma, and L. platydorsus), and (3) lacustrine spawners (L. crassibarbis, L. dainellii, L. gorgorensis, L. gorguari, L. longissimus, L. nedgia, and L. surkis). Generalists and lacustrine spawners most probably spawn in the littoral and adjacent floodplains of Fogera and Dembea; however, their actual breeding ground should be investigated to implement sound management options. To sustain the riverine Labeobarbus spawners, closing the gillnet fishery from August to October in the rivers and river mouths is believed to be necessary. Keywords: endemic, fecundity, Labeobarbus, Lake Tana, reproduction, spawning migration
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    Species Composition, Relative Abundance and Socio-Economic Value of Fishes in Ribb and Gumara River, Eastern Lake Tana
    (Addis Ababa University, 2016-09) Shumye, Yeshizerf; Getahun, Abebe (PhD)
    This study was carried out in the eastern part of Lake Tana (Fogera Woreda) covering both postrainy and dry seasons, from October 2015 to April 2016, with the objective to identify and assess species composition, relative abundance, socio-economic and marketing system of fish and fisheries in that locality. Field sampling, personal observation, structured questionnaire and interview were employed. Shannon diversity index was used to compare species diversity in all sampling sites between seasons. Correlation analysis and paired T- test were used to test species composition and abundance between seasons. Descriptive analysis and two ways ANOVA were used to analyze the collected data. Generally eight fish species were identified and Cyprinidae are the dominate one. Species composition of the fishes during the post- rainy and dry seasons was different. Mean Shannon diversity index showed highest H’ value (1.06) in dry than postrainy (1.04) season. The relative abundance score of species during the post-rainy and dry seasons was variable in all sampling sites and in dry season higher numbers of species were recorded (114). However, the most abundant species was Labeobarbus crassibarbus in weight (43.1) and Labeobarbus intermedius (46.7%) in number. Relation of fishing categories to boat and daily catch was analyzed by two way ANOVA and daily catch of fishers to the type of boat showed a significant difference (P<0.05). The fish price was influenced by marketing site, season and demand of customers. The Univariance analysis showed that there is significant difference (P<0.05) in price around landing site and Woreta city as well as in fasting and none fasting x periods. The finding of this thesis indicated that, training on fishing management, availability of infrastructure (road), access to credit and minimizing illegal fishing would promote effective fish resource utilization and sustainable market. Keywords: Fish price, Gumara River, Lake Tana, Relative abundance, Ribb River, Socio- Economics, Species composition