Cage aquaculture is rapidly expanding in Lake Victoria, Kenya, yet its effects on native biodiversity remain poorly understood. This study assessed the impacts of cage aquaculture on wild fish and zooplankton communities by comparing biodiversity indices between experimental cage and control sites between March and August 2024. This study was conducted at the Rasira cages site in Lake Victoria, Kenya. Wild broodstock of Oreochromis esculentus were collected from Gesebei, Nyamira County whereas Oreochromis variabilis were collected from Oki and Kanyaboli dams in Homa Bay and Siaya County. They were transported to the Kenya Marine and Fisheries Research Institute where they were quarantined for 30 days followed by stocking and pairing in a ratio of 3:1 in 200 m2 multiplication pond. After three weeks, fingerlings were collected, stocked in nursery ponds, and fed 45% CP starter feeds until they attained 5 ± 0.01 g where they were conditioned, transported and stocked in the cages at a density of 83 fish/m3. Wild fish were sampled using experimental gill nets, while zooplankton were collected using standard plankton nets to collect data on species biodiversity. Shannon-Wiener diversity indices were calculated for both communities. Results showed that Two-Way ANOVA presented a significant difference between the sampling periods for the two communities (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 pattern shifted in August with cage sites showing lower diversity (H’ = 0.65 ± 0.27) dominated by haplochromine cichlids (81%). Zooplankton communities were dominated by copepods at both sites, with Cyclopoida comprising 51% - 78% of total density. Species composition shifted between sampling periods, with Thermocyclops showing increased dominance near cages. These findings suggest that cage aquaculture alters local biodiversity patterns, with seasonal variations in fish community structure and potential nutrient enrichment effects on zooplankton. Management strategies should incorporate biodiversity monitoring to ensure sustainable cage aquaculture development in Lake Victoria.
References
[1]
Hecky, R.E., Mugidde, R., Ramlal, P.S., Talbot, M.R. and Kling, G.W. (2010) Multiple Stressors Cause Rapid Ecosystem Change in Lake Victoria. Freshwater Biology, 55, 19-42. https://doi.org/10.1111/j.1365-2427.2009.02374.x
[2]
Cadwalladr, D.A. (1965) The Decline of Labeovictorianus (Pisces: Cyprinidae) Fishery of Lake Victoria and Associated Deterioration in Some Indigenous Fishing Methods in the Nzoia River, Kenya. East African Agricultural and Forestry Journal, 30, 249-256. https://doi.org/10.1080/00128325.1965.11661990
[3]
Ogutu-Ohwayo, R., Hecky, R.E., Cohen, A.S. and Kaufman, L. (1997) Human Impacts on the African Great Lakes. Environmental Biology of Fishes, 50, 117-131. https://doi.org/10.1023/a:1007320932349
[4]
Goldschmidt, T., Witte, F. and Wanink, J. (1993) Cascading Effects of the Introduced Nile Perch on the Detritivorous/Phytoplanktivorous Species in the Sublittoral Areas of Lake Victoria. Conservation Biology, 7, 686-700. https://doi.org/10.1046/j.1523-1739.1993.07030686.x
[5]
Nagl, S., Tichy, H., Mayer, W.E., Takezaki, N., Takahata, N. and Klein, J. (2000) The Origin and Age of Haplochromine Fishes in Lake Victoria, East Africa. Proceedings of the Royal Society of London. Series B: Biological Sciences, 267, 1049-1061. https://doi.org/10.1098/rspb.2000.1109
[6]
Njiru, J.M., Aura, C.M. and Okechi, J.K. (2019) Cage Fish Culture in Lake Victoria: A Boon or a Disaster in Waiting? Fisheries Management and Ecology, 26, 426-434. https://doi.org/10.1111/fme.12283
[7]
Kenya Marine and Fisheries Research Institute (KMFRI), Aquaculture Business De-velopment Programme (ABDP), Kenya Fisheries Service (KeFS) and State Depart-ment for Fisheries, Aquaculture and the Blue Economy (SDFA & BE) (2022) Sustainable Community-Based Cage Aquaculture in Lake Victoria, Kenya (Technical Report, May 2022). Aquaculture Business Development Programme. https://www.abdpcu.org/wp-content/uploads/2023/07/Community-based-cage-report_30-05-2022.pdf
[8]
Republic of Kenya, Ministry of Mining, Blue Economy and Maritime Affairs, State Department for the Blue Economy and Fisheries (2025) National Aquaculture Pol-icy 2025 [Draft Policy Document]. Government of Kenya.
[9]
Okechi, J.K., Peoples, N., Nyamweya, C.S., Glaser, S. and Kaufman, L. (2022) The Ecological Health of Lake Victoria (Kenya) in the Face of Growing Cage Aquaculture. Conservation Science and Practice, 4, e12826. https://doi.org/10.1111/csp2.12826
[10]
Dauda, A.B., Ajadi, A., Tola-Fabunmi, A.S. and Akinwole, A.O. (2019) Waste Production in Aquaculture: Sources, Components and Managements in Different Culture Systems. Aquaculture and Fisheries, 4, 81-88. https://doi.org/10.1016/j.aaf.2018.10.002
[11]
Sweke, E.A., Assam, J.M., Chande, A.I., Mbonde, A.S., Mosha, M. and Mtui, A. (2016) Comparing the Performance of Protected and Unprotected Areas in Conserving Freshwater Fish Abundance and Biodiversity in Lake Tanganyika, Tanzania. International Journal of Ecology, 2016, 1-7. https://doi.org/10.1155/2016/7139689
[12]
Kashindye, B.B., Nsinda, P., Kayanda, R., Ngupula, G.W., Mashafi, C.A. and Ezekiel, C.N. (2015) Environmental Impacts of Cage Culture in Lake Victoria: The Case of Shirati Bay-Sota, Tanzania. SpringerPlus, 4, Article No. 475. https://doi.org/10.1186/s40064-015-1241-y
[13]
Okechi, J.K., Peoples, N., Nyamweya, C.S., Orina, P.S., Cooperman, M.S. and Kaufman, L. (2025) Effects of Nile Tilapia (Oreochromis niloticus) Cage Aquaculture on Water Quality in the World’s Largest Tropical Lake. Journal of Great Lakes Research, 51, Article 102576. https://doi.org/10.1016/j.jglr.2025.102576
[14]
Dias, J.D., Takahashi, É.M., Santana, N.F. and Bonecker, C.C. (2011) Impact of Fish Cage-Culture on the Community Structure of Zooplankton in a Tropical Reservoir. Iheringia. Série Zoologia, 101, 75-84. https://doi.org/10.1590/s0073-47212011000100011
[15]
Enawgaw, Y., Wagaw, S., Wosnie, A. and Tessema, K. (2023) Zooplankton as Ecosystem Indicators and Their Effects on Eutrophication in Lake Arekit (Ethiopia) —Implication for Freshwater Habitat Management. Journal of Freshwater Ecology, 38, Article 2287433. https://doi.org/10.1080/02705060.2023.2287433
[16]
Musa, S., Aura, C.M., Tomasson, T., Sigurgeirsson, Ó. and Thorarensen, H. (2022) Impacts of Nile Tilapia Cage Culture on Water and Bottom Sediment Quality: The Ability of an Eutrophic Lake to Absorb and Dilute Perturbations. Lakes & Reservoirs: Science, Policy and Management for Sustainable Use, 27, e12413. https://doi.org/10.1111/lre.12413
