Browsing by Author "Lemma, Brook (Professor)"
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Item Fish Biology and Fishery Management of Commercial Stocks in a Tropical Rift Valley Lake, Lake Langeno, Ethiopia(Addis Ababa University, 2018-03-05) Temesgen, Mathewos; Getahun, Abebe (Professor); Lemma, Brook (Professor)The study of status and trends of fish and fisheries in Lake Langeno (also known in the literature as Langano), Ethiopia was conducted from March 2014 to February 2016. The basis for this study was that fish stocks were subjected to uncontrolled fishing over many years and available data on the status and trends of fishes in the lake has become unreliable for management and sustainability of the sector. In order to examine the diversity, habitat preference and seasonal distribution, spatial and seasonal data were collected from six different sampling sites by using gillnets of various mesh sizes and long lines. Data were analyzed by Canonical Correspondence Analysis (CCA), SPSS software and by various descriptive statistics. The results indicate physico-chemical parameters showed no significant spatial variation, but high seasonal variation. A total of seven fish species dominated by family Cyprinidae were identified (H’=1.264). Carassius carassius, was not reported in previous studies, now comprise 0.64% of the total collected specimens. All the fish species were collected from all of the sampling sites, except at one site (Middle), where Carrasius carassius and Garra dembecha were absent. Index of relative importance (IRI) was essentially similar for all the sampling sites, but differed in the relative importance of each species with the high importance of Oreochromis niloticus. Principal Component Analysis (PCA) did not produce distinct habitat-associated species patterns across the sampling sites. However, temperature and depth seemed to be the key environmental factors determining fish community structure in the lake. The results showed that the composition of the fishes has undergone some changes during data collection from what was reported in the literature. The Length-weight relationships of O. niloticus, E. paludinosus, C. gariepinus, L. intermedius and C. carpio were curvilinear (b=2.872, 2.554, 2.823, 2.771 and 2.919, respectively), and statistically significant (p>0.05) except for Enteromius paludinosus. For both sexes, the mean Fulton Condition Factor values of Oreochromis niloticus, B. paludinosus, Clarias gariepinus, Labeobarbus intermedius and C. carpio were 1.77 }0.37, 1.06 }0.44, 0.60 }0.5, 1.33 }0.44 and 1.47 }0.83, respectively. A better body condition was recorded in the dry seasons for all species except for O. niloticus. All fish species had relatively smaller maximum size and poor body condition than what was reported for fishes in most of the Ethiopian water bodies. Females were more abundant than males for all fish species, and the sex ratio of O. niloticus (1.13:1)and E. paludinosus (1:.24:1) was significantly different from the hypothetical distribution of 1:1 (χ2, p<0.05. The identified peak breeding time was April- June, May-July, June-July and March-May for O. niloticus, C. gariepinus, L. intermedius and C. 5 carpio, respectively. Their respective length at L50 for females and males during these breeding times were 16.4 cm & 15.8 cm TL, 28.5 cm & 29.5 cm TL 30.5 cm & 29.5 cm FL and 28.2 cm & 27.6 cm FL. The mean fecundity of these fish species were 463.83 }114, 141,466 }40,982, 3,055 }2,234 and 105,631 }46,680, respectively. The results also showed significant seasonal variations of GSI for all fish species (ANOVA, P< 0.05). In addition, seven food items, namely phytoplankton, zooplankton, insects, detritus, macrophytes, fish parts and nematodes were identified from the stomach contents of O. niloticus. Phytoplankton was the main food grazed followed by detritus, zooplankton and macrophytes. The other food items were occasionally and randomly consumed. The volumetric contribution of these food items showed high variation in the study months (p<0.05). Phytoplankton and detritus were the dominant food items in the dry season and zooplankton and macrophytes were the highest in the wet months. The contribution of phytoplankton, zooplankton and insects were slightly high in small sized groups (<10 cm), whereas detritus, macrophytes and fish parts were the highest in larger size groups (>20 cm). Generally, food items of plant origin dominated the stomach contents, typically associated with less protein content than food item of animal origin. The result also showed that the lake supported small-scale beach seine fishery for small income generation and alternative employment opportunity of fishermen. The catch composition was dominated by O. niloticus (87.58%) followed by C. gariepinus (5.89%). Fisheries value chain was also developed and major related issues were addressed, fishers’ perceptions about the resources condition and management status were identified and discussed. Generally, the total annual fish production from the lake was estimated to be 1,137.67 tonnes/ year, and the mean gross annual revenue was about 8,622,158 ETB. Extrapolation of annual production and annual revenue from the sector showed a significance variation among the landing facility owners and those that do not have landing facilities (ANOVA, p<0.05), and between the fulltime and part time fishermen (ANOVA, p<0.05). The estimated annual per capita consumption of fish/ person was about 23.65 kg. The majority of the fishermen had positive attitude towards the fish resources, but due to lack of knowledge and follow up, the current harvest system and fishing methods put these resources at risk. Therefore, appropriate management action should be in place in order to sustain the fish resources in Lake Langeno.Item Fish Biology and Fishery Management of Commercial Stocks in a Tropical Rift Valley Lake, Lake Langeno, Ethiopia(Addis Ababa University, 3/5/2018) Temesgen, Mathewos; Getahun, Abebe (Professor); Lemma, Brook (Professor)The study of status and trends of fish and fisheries in Lake Langeno (also known in the literature as Langano), Ethiopia was conducted from March 2014 to February 2016. The basis for this study was that fish stocks were subjected to uncontrolled fishing over many years and available data on the status and trends of fishes in the lake has become unreliable for management and sustainability of the sector. In order to examine the diversity, habitat preference and seasonal distribution, spatial and seasonal data were collected from six different sampling sites by using gillnets of various mesh sizes and long lines. Data were analyzed by Canonical Correspondence Analysis (CCA), SPSS software and by various descriptive statistics. The results indicate physico-chemical parameters showed no significant spatial variation, but high seasonal variation. A total of seven fish species dominated by family Cyprinidae were identified (H’=1.264). Carassius carassius, was not reported in previous studies, now comprise 0.64% of the total collected specimens. All the fish species were collected from all of the sampling sites, except at one site (Middle), where Carrasius carassius and Garra dembecha were absent. Index of relative importance (IRI) was essentially similar for all the sampling sites, but differed in the relative importance of each species with the high importance of Oreochromis niloticus. Principal Component Analysis (PCA) did not produce distinct habitat-associated species patterns across the sampling sites. However, temperature and depth seemed to be the key environmental factors determining fish community structure in the lake. The results showed that the composition of the fishes has undergone some changes during data collection from what was reported in the literature. The Length-weight relationships of O. niloticus, E. paludinosus, C. gariepinus, L. intermedius and C. carpio were curvilinear (b=2.872, 2.554, 2.823, 2.771 and 2.919, respectively), and statistically significant (p>0.05) except for Enteromius paludinosus. For both sexes, the mean Fulton Condition Factor values of Oreochromis niloticus, B. paludinosus, Clarias gariepinus, Labeobarbus intermedius and C. carpio were 1.77 }0.37, 1.06 }0.44, 0.60 }0.5, 1.33 }0.44 and 1.47 }0.83, respectively. A better body condition was recorded in the dry seasons for all species except for O. niloticus. All fish species had relatively smaller maximum size and poor body condition than what was reported for fishes in most of the Ethiopian water bodies. Females were more abundant than males for all fish species, and the sex ratio of O. niloticus (1.13:1)and E. paludinosus (1:.24:1) was significantly different from the hypothetical distribution of 1:1 (χ2, p<0.05. The identified peak breeding time was April- June, May-July, June-July and March-May for O. niloticus, C. gariepinus, L. intermedius and C. 5 carpio, respectively. Their respective length at L50 for females and males during these breeding times were 16.4 cm & 15.8 cm TL, 28.5 cm & 29.5 cm TL 30.5 cm & 29.5 cm FL and 28.2 cm & 27.6 cm FL. The mean fecundity of these fish species were 463.83 }114, 141,466 }40,982, 3,055 }2,234 and 105,631 }46,680, respectively. The results also showed significant seasonal variations of GSI for all fish species (ANOVA, P< 0.05). In addition, seven food items, namely phytoplankton, zooplankton, insects, detritus, macrophytes, fish parts and nematodes were identified from the stomach contents of O. niloticus. Phytoplankton was the main food grazed followed by detritus, zooplankton and macrophytes. The other food items were occasionally and randomly consumed. The volumetric contribution of these food items showed high variation in the study months (p<0.05). Phytoplankton and detritus were the dominant food items in the dry season and zooplankton and macrophytes were the highest in the wet months. The contribution of phytoplankton, zooplankton and insects were slightly high in small sized groups (<10 cm), whereas detritus, macrophytes and fish parts were the highest in larger size groups (>20 cm). Generally, food items of plant origin dominated the stomach contents, typically associated with less protein content than food item of animal origin. The result also showed that the lake supported small-scale beach seine fishery for small income generation and alternative employment opportunity of fishermen. The catch composition was dominated by O. niloticus (87.58%) followed by C. gariepinus (5.89%). Fisheries value chain was also developed and major related issues were addressed, fishers’ perceptions about the resources condition and management status were identified and discussed. Generally, the total annual fish production from the lake was estimated to be 1,137.67 tonnes/ year, and the mean gross annual revenue was about 8,622,158 ETB. Extrapolation of annual production and annual revenue from the sector showed a significance variation among the landing facility owners and those that do not have landing facilities (ANOVA, p<0.05), and between the fulltime and part time fishermen (ANOVA, p<0.05). The estimated annual per capita consumption of fish/ person was about 23.65 kg. The majority of the fishermen had positive attitude towards the fish resources, but due to lack of knowledge and follow up, the current harvest system and fishing methods put these resources at risk. Therefore, appropriate management action should be in place in order to sustain the fish resources in Lake Langeno.Item Limnological Studies on Lake Tinishu Abaya, Ethiopia(Addis Ababa University, 2019-06-02) Enawgaw, Yirga; Lemma, Brook (Professor)Lake Tinishu Abaya, hereafter referred to as LTA, is a small-sized inland water body in the rift valley system of Ethiopia. LTA was stocked with Tilapia fish (Oreochromis niloticus) in 1997 to enhance fishery and provide animal protein source to the local community. This study designed to investigate the limnological features (physical, chemical, and biological) of the lake and determine the ecological productivity, water quality, and its potential service for users in the neighborhood and the nation at large. Moreover, the baseline information from the study can be used by policymakers to design strategies for sustainable use of LTA. All the data for this study were collected and analyzed using standardized sampling techniques and methods. The water samples for the analyses of physicochemical parameters, phytoplankton, and zooplankton were collected monthly between January and December 2016 from two selected sampling sites (open water and shore area). Benthic macroinvertebrates were collected from March to August 2017 from five sampling sites. For analysis of fish gut content and related studies, O. niloticus fish samples were collected from March to May and July to September in 2017. The results of the various physicochemical parameters suggested that LTA was well oxygenated, slightly warm, and alkaline. From the values of conductivity (as a proxy to salinity) the lake can be classified as a freshwater body compared some other rift valley lakes of Ethiopia and TDS values. TDS of LTA was always less than 3000 mgL-1 indicating freshwater system. The water of LTA was turbid, low water clarity, shallow euphotic area, and hypertrophic state with nutrient enrichment. In LTA, 37 phytoplankton taxa belonging to six groups were found. Bacillariophyceae (40%) were the most diversified phytoplankton followed by Chlorophyceae (30%), Cyanobacteria (19%), Euglenophyceae (5%), Dinophyceae (3%), and Cryptophyceae (3%). In this study, 24 zooplankton taxa comprising of rotifers, cladocerans, and copepods were recorded. The abundance of zooplankton was dominated by copepods (54%) followed by rotifers (40%). The overall mean total standing biomass of zooplankton was 230.87 in open water and 164.2 μg L-1 at shore area, and it was broadly dominated (94%) by the microcrustaceans (copepods & cladocerans). The photosynthetic productivity of phytoplankton of LTA was determined in the open water, and the results showed that the rate of photosynthesis (Amax) ranged from 0.62 g C m-3 h-1 to 2.02 g C m-3 h-1. The hourly integral photosynthetic production (ΣA) and pattern of variation for the daily integral rates of photosynthesis (ΣΣA) ranged from 0.247 g C m-2 h-1 to 1.022 g C m-2 h-1 and 5.43 g C m-2 d-1 to 9.194 g C m-2 d-1, respectively. Because of the number of phytoplankton and zooplankton taxa, their abundance, and biomass, and considering marked values of photosynthetic productivity it was concluded that LTA is biologically productive aquatic resource to support fish and other aquatic organisms. The ecological condition of LTA was assessed using benthic macroinvertebrates as well, and a total of 5735 benthos specimens comprising of 23 taxa were collected from all the study sites. There was a spatial effect on the distribution of benthic individuals (ANOVA; p <0.05). It was high at Dacha riverside (n=2089) followed by Bobodo riverside (n=1145), Reference site (n= 963), Badober riverside (n= 859), and Main fish landing site (n=679). The Hemiptera family were the predominant macroinvertebrates that contributed the largest number (n=2546) of the total samples followed by Diptera (n=878), Coleoptera (n=835, 14.56%) and Gastropods (n=631). The majority (about 70%) of the benthic communities of LTA comprised pollution tolerant species as compared to pollution sensitive ones. This indicated the existence of organic pollution, and thus LTA is undergoing environmental stresses. The diet and other related aspects of the stocked O. niloticus were also assessed. The relationship between the total length and standard length of O. nilotucus in LTA was linear and significant (R² =0.962, TL=0.1456SL+1.8088). The relationship between total length and the total weight of O. niloticus, on the other hand, was curvilinear with a strong relationship (R²= 0.9848, TW =0.0194 TL2.9876). The slope of the regression (b) was 2.9876, closer to the isometric growth value (b=3) of fish. The Fulton´s Condition Factor (FCF) of O. niloticus ranged from 0.96 to 3.51 (mean= 1.88). The well being of O. niloticus fish showed that the majority of the population in LTA were in good condition (FCF >1). Phytoplankton, detritus, zooplankton, and macrophytes were the most important food items while insects, nematodes, ostracods, and fish scales made up minor portions of the diet of O. niloticus in LTA. The importance of phytoplankton, macrophytes, and detritus increased with increasing fish-size and the significance of zooplankton, insects, and other animal origin food items declined with increasing fish size. In a nutshell, LTA is a productive lake and an important aquatic resource for the surrounding area. But the lake and its watershed are facing many threats from intensive human activity. The major problems affecting LTA include excessive water abstraction, extensive shoreline modification, sedimentation, eutrophication, water pollution due to organic waste from agricultural area and overfishing. At the same time, efforts to ensure the health and normal functioning of this productive ecosystem are negligible. Thus, management solutions should be developed to avert the current and continuing degradation of LTA and its environs. Some of the actions that should be taken, but not limited to, are: demarcating a buffer zone, restoration of riparian habitats, regulating the excessive water abstraction, controlling mass fish catching, and empowering the local community to protect and conserve this aquatic resource.Item Studies on Zwai Wetlands as Reservoirs of Gastrointestinal Parasites of Sheep and Humans and as Habitats of Snail Vectors.(Addis Ababa University, 2019-10-10) Sisay, Ayalew; Lemma, Brook (Professor)In tropical countries like Ethiopia where the wet seasons are restricted to less than five months of the year, wetlands such as those found around Lake Zwai provide ideal environments for water-related diseases of sheep and humans. As a consequence, this study was conducted over a 2-year period to study the gastro-intestinal parasites of sheep and humans (schoolchildren) that frequently visit the wetlands of Lake Zwai, the intermediate hosts (snails) inhabiting the same wetlands and the effectiveness of drugs on the gastro-intestinal parasites identified in the wetlands. The results generally showed that the wetlands of Lake Zwai are infested with gastro-intestinal parasites as shown in the tracer animals used (sheep) and by a different set of parasites picked by schoolchildren visiting the same wetlands. The snail vectors surveyed in these wetlands were generally found to host the diseases of the sheep rather than those diseases of the schoolchildren. The drug effectiveness trials conducted of the livestock gastro-intestinal nematode parasites were found to be susceptible in Tetramizole and Ivermectine, with lower resistance in only one drug (Albendazole). It was concluded that Zwai wetlands that provide fresh herbage to sheep throughout the year and attractive playing grounds to schoolchildren of a nearby school, provide conducive environments mostly to waterborne gastro-intestinal parasites of sheep and to a lesser extent to humans (schoolchildren). In all cases of the definitive hosts (sheep and humans), their performance in life is severely affected, if in rare cases deaths do not occur. It was, therefore, recommended that visits of sheep and humans to the wetlands should be restricted particularly at peak infection months, inflow of animal wastes with parasite eggs be diverted for treatment, regimes of prophylactic treatments should be introduced and generally awareness of the disease cycles, herbages for animals should be collected and treated before feeding the sheep, safe wetland playing-grounds for schoolchildren should be identified and safe wastehandling methods should be introduced into the local population and sheep owners.