The functional role of fish diversity in Lake Victoria, East Africa (Uganda, Tanzania, Kenya)

Lake Victoria, the world's largest tropical lake, is home and provides livelihood to millions of East Africans. Historically it contained 500+ species of indigenous fishes, most of which were haplochromine cichlids. The 1959–60 introduction of the predatory fish Nile perch (Lates niloticus), coupled with other sources of environmental degradation, caused the extinction of hundreds of cichlid species. The resultant L. niloticus fishery, now the world's largest freshwater fishery, gained popularity as a food and revenue source for the East African nations, often overshadowing concerns regarding cichlid conservation. This study examined functional roles of fish diversity in Lake Victoria using field, laboratory, and modeling techniques. I hypothesized that fish diversity was related to community function.; In the laboratory I found that Nile perch captured cichlids ( Haplochromis “ruby”) more easily than schooling cyprinids (Brachydanio rerio) at several predator, and prey densities. Increased expenditures in active metabolism, such as increased feeding costs, can negatively impact growth. I related dietary correlated changes in Nile perch growth to changes in activity and consumption using a bioenergetics model. The loss of cichlids from the Nile perch diet may affect activity and consumption, with varying consequences for growth efficiency.; The effects of fish diversity on system throughput were investigated using a dynamic mass-balance model. Haplochromine stock sizes impacted total system detritivory and phytoplanktivory. The restoration of cichlid diversity may benefit system function.; Metabolic variance was described in two cichlid species (Xystichromis phytophagus and Pyxichromis orthostoma) and their F2 hybrid. For the hybrid, standard metabolic rates and surface to volume ratios of digestive and respiratory organs were intermediate of the parentals. Metabolic diversity may be heritable and can govern the potential functional roles of cichlids.; Fish communities were studied in the Lake Kyoga system in central Uganda. The system contains diverse pristine cichlid lakes and disturbed Nile perch lakes. Stable nitrogen isotopic signatures suggested that Nile perch have altered food webs in the Kyoga system much like they have in Lake Victoria. The Kyoga satellite system represents a natural experiment for further investigating the functional role of fish diversity in Lake Victoria.