Department of Biology

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    STUDIES ON THE REPRODUCTIVE BIOLOGY AND FEEDING HABITS OF SOME FISH SPECIES AND DETERMINATION OF SOME PHYSICO-CHEMICAL CHARACTERISTICS OF LAKE BOYO, ETHIOPIA
    (Hawassa University, 2024-11) TAMIRAT HANDAGO SADE
    Lake Boyo is among the few neglected and unexplored small lakes in the Central Ethiopian Rift Valley Region. It is a shallow and turbid lake with surface area of 3.2 square kilometres and surrounded by wetland. Three fish species are known to exist in the lake, namely Nile Tilapia Oreochromis Niloticus (Linnaeus, 1758), the straightfin barb Enteromius paludinosus (Peters 1852) and the lapping minnow Garra quadrimaculata (Rüppell, 1835). Neither fishery activity nor fishery research has ever been conducted so far in Lake Boyo. This research was conducted to provide baseline information on some aspects of the reproductive biology and feeding habits of fish species, and physicochemical characteristics of the lake. All the data for this study were collected and analyzed using standardized methods and sampling techniques. For the analysis of reproductive biology and feeding habits, samples of the three fish species were collected from two sites (littoral and open) of the eastern part of the lake from May 2021 to May, 2022 using gill nets of 6, 8, and 10 cm mesh size and a beach seine of 6 mm mesh size. A total of 379 O. niloticus, 513 E. paludinosus, and 290 G. quadrimaculata samples were examined. The water samples for the analyses of physicochemical parameters were collected from two selected sampling sites (littoral and open water area) in wet months (June to September), and dry months (October to December) of 2022. The three fish species breed throughout the year and showed a bi-modal major and minor breeding period. The first peak breeding months occur from February to March and the second minor peak from July to September for O. niloticus, whereas the main breeding season for E. paludinosus was between October and January with a less pronounced reproductive period between March and April. On the otherhand, the first peak breeding period was from June to September and the second peak from January to February for G. quadrimaculata. The fecundity of O.niloticus ranged from 216 to 1,157 eggs per fish while it ranged from 1,078 to 9,683 eggs per fish for E. paludinosus. The result of length at first maturity (Lm50) depicted that the fishes reached sexual maturity at a smaller size and shows early maturity of all the fish species in the lake. The results of the analysis of sex ratio for the fish species examined showed that the distribution of male and female fishes in the lake was not significantly different from the hypothetical 1:1(Male: Female) ratio for O. niloticus and E. paludinosus (1:0.92, p>0.05 and 1:1.03, p>0.05, respectively), while it was significantly different for G. quadrimaculata (1: 0.73, p<0.05). The results of the length weight relationship (LWR) of the fish species suggested a curvilinear relationship (R2= 0.9911, 0.9812 and 0.9766 for O.niloticus, E. paludinosus and G. quadrimaculata, respectively) and, a positive allometric growth pattern (b= 3.1268 and 3.1042 for O.niloticus, E. paludinosus, respectively) while nearly isometric growth pattern (b= 2.977) for G. quadrimaculata. The result of Fulton`s conditon factor (FCF) for the fish species revealed that O.niloticus and E. paludinosus had moderate body condition (FCF= 1.73 and 1.77 for males and females of O.niloticus, respectively, and 1.21 and 1.27 for males and females of E. paludinosus, respectively), while it was low for G. quadrimaculata (FCF= 0.011 and 0.0112 for males and females, respectively). The feeding habits of the fish species showed that the fishes feed on a variety of food items including detritus, phytoplankton, macrophytes, insects and zooplankton and they are ominivorous in their feeding habits. Detritus was the main food item for the fish species in general. The fishes showed seasonal variations in feeding habits during the dry and wet months. From these results it was concluded that the fishes are omnivorous in Lake Boyo. The results of the physical and chemical features of the lake shows that the lake water was slightly warm, alkaline, contained more TDS and EC, very turbid, low transparency and with relatively high inorganic nutrients (NO3- and PO4 3-) which support most of the aquatic life. Generally, based on the results it is concluded that Lake Boyo is a low productive inland freshwater ecosystem in the Ethiopian Rift Valley basin. The high amount of detritus in the stomachs/guts of the fishes and lower condition factor of the fish with reference to other lakes indicate that productivity of Lake Boyo is low. Further research is recommended on macrophyte, phytoplankton and zooplankton composition, biomass and productivity of Lake Boyo.