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dc.contributor.advisorDr. Seyoum Mengistouen_US
dc.contributor.authorGhebrai, Afeworki-
dc.descriptionA Thesis Submitted to the School of Graduate Studies, Addis Ababa University In Partial Fulfilment of the Requirements for the Degree of Master of Science in Biology.en_US
dc.description.abstractStudies on the species composition, age structure, sex ratio, pattern of abundance and measurement of body size and brood size was performed on the zooplankton community in Lakes Bishoftu and Arenguade from January 1991 to December 199 the former is inhabited by planktivorous fish, Aplocheilichthys and Sp oreochromis niloticus while the latter is devoid of fish. The species composition of the zooplankton community in the species composition of the zooplankton community in both lakes is poorly diverse and share a dominant calartoid, Lovenula (Pardiaptomus) africana (Daday, 1908) and one dominant rotifer genus Brachionus. Additionally Lake Bishoftu is inhabited by the cylopoid Mesocyclops aequatorialis. Body size and brood size of ovigerous females of L.africana from these lakes were significantly different both in body size and mean brood size (P <0,001). The frequency distribution of the adult size classes is negatively skewed in Lake Bishoftu as opposed to Lake Arenguade. Body size• and brood size were positively related in both lakes and strongly positive (R = 0.447) in the population under predation pressure than with no predation (R = 0.297). Most size classes of Lake Bishoftu’s copepods bear significantly different mean brood size (GT2 test). Sex ratio was also significantly different from the expected one to one ratio in both lakes (P < 0,001) and the ratio is strongly skewed in favour of females in Lake Arenguade. Also a higher proportion of adults to juveniles was observed in the latter. Seasonal variation in body and, brood size were also observed in relation to the mixing period (November - February) and fish kill the differences in. body and brood siz were attributed to size selective production by fish in Bishoftu, absence of competition food .limitation and temperature differences between the two lakes. One factor ANOVA revealed that zooplankton abundance differed significantly between moths (P < 0.001). Except for rotifers, zooplankton biomass showed• clear seasonality with population collapse during the mixing period coinciding with upwelling of anoxic water and H,S. Recovery and peak abundance were observed during the stratification period ( July - September). Rate of recovery was variable for different• species and stages. Phytoplankton and major nutrients showed less pronounced seasonality in both lakes, with nitrogen rather than phosphorous being more limiting.en_US
dc.description.sponsorshipAddis Ababa Universityen_US
dc.publisherAddis Ababa Universityen_US
dc.titleZooplanktonStructure and Dynamics in two Contrasting Soda Lakes. (Debre Zeit Crater Lakes: Ethiopiaen_US
Appears in Collections:Thesis - Biology

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