Effects of Cage Aquaculture on Biodiversity of Lake Victoria, Kenya

Cage aquaculture is rapidly expanding in Lake Victoria, Kenya, yet its effectson native biodiversity remain poorly understood. This study assessed the im-pacts of cage aquaculture on wild fish and zooplankton communities by com-paring biodiversity indices between experimental cage and control sites be-tween March and August 2024. This study was conducted at the Rasira cagessite in Lake Victoria, Kenya. Wild broodstock of Oreochromis esculentus werecollected from Gesebei, Nyamira County whereas Oreochromis variabilis werecollected from Oki and Kanyaboli dams in Homa Bay and Siaya County. Theywere transported to the Kenya Marine and Fisheries Research Institute wherethey were quarantined for 30 days followed by stocking and pairing in a ratioof 3:1 in 200 m2 multiplication pond. After three weeks, fingerlings were col-lected, stocked in nursery ponds, and fed 45% CP starter feeds until they at-tained 5 ± 0.01 g where they were conditioned, transported and stocked in thecages at a density of 83 fish/m3. Wild fish were sampled using experimentalgill nets, while zooplankton were collected using standard plankton nets tocollect data on species biodiversity. Shannon-Wiener diversity indices werecalculated for both communities. Results showed that Two-Way ANOVA pre-sented a significant difference between the sampling periods for the two com-munities (p < 0.05). Fish diversity was higher at cage sites (H’ = 1.33 ± 0.58)compared to control sites (H’ = 0.99 ± 0.43) during March, but this patternshifted in August with cage sites showing lower diversity (H’ = 0.65 ± 0.27) dominated by haplochromine cichlids (81%). Zooplankton communities weredominated by copepods at both sites, with Cyclopoida comprising 51% - 78%of total density. Species composition shifted between sampling periods, withThermocyclops showing increased dominance near cages. These findings sug-gest that cage aquaculture alters local biodiversity patterns, with seasonal var-iations in fish community structure and potential nutrient enrichment effectson zooplankton. Management strategies should incorporate biodiversity mon-itoring to ensure sustainable cage aquaculture development in Lake Victoria.

Keywords Cage Aquaculture, Biodiversity, Lake Victoria, Zooplankton, HaplochromineCichlids, Shannon-Wiener Index