In situ Captive Growth Performance and Conservation Potential of Native Tilapiines in Lake Victoria, Kenya: A Case Study of Rasira Beach

Tonny Orina Sagwe*, Robert Nesta Kagali, Kevin Mbogo, Michael S Cooperman, Les Kaufman, John Okechi, Paul Sagwe Orina and Mercy Chepkirui

The endangered native tilapiine cichlids Oreochromis variabilis and Oreochromis esculentus have declined dramatically in Lake Victoria due to introduced species, overfishing, and habitat degradation. This study evaluated the potential of cage aquaculture as an ex-situ conservation tool for these species by assessing growth performance, survival, natural reproduction, and water quality impacts under controlled cage conditions in Lake Victoria, Kenya. A six-month completely randomized experiment was conducted using 8 m³ cages stocked with 30 fish m⁻³ (initial weight 5 ± 0.01 g) at Rio Fish Farm, Homa Bay County. Oreochromis niloticus served as a comparative reference. Growth performance differed significantly among species (two-way ANOVA, species effect:  F_{(2, 24)} = 124.7, p < 0.001). O. niloticus attained the highest final weight (185.39 ± 0.93 g), whereas O. variabilis (47.26 ± 5.25 g) and O. esculentus (46.03 ± 1.99 g) grew more slowly (Tukey’s HSD, p < 0.001 for both comparisons). Feed conversion ratios (FCR) were significantly lower for O. niloticus (1.77) compared to O. variabilis (5.26) and O. esculentus (5.48) (Tukey’s HSD, p < 0.001). Survival rates were high across all species: O. niloticus (88.55%), O. esculentus; (85.55%), and O. variabilis (75.9%), with significantly lower survival in O. variabilis compared to O. niloticus (Tukey’s HSD, p = 0.018). Critically, fry of both native species were observed throughout the trial, indicating successful natural spawning under cage conditions, a key finding for conservation breeding. Water quality monitoring revealed significantly elevated total nitrogen (up to 463.5 ± 54.7 µg L⁻¹; p = 0.008) and total phosphorus (up to 41.5 ± 2.2 µg L⁻¹; p = 0.042) at cage sites compared to open water controls. We conclude that cage aquaculture offers a viable pathway for ex-situ conservation of O. variabilis and O. esculentus, particularly through captive breeding and stock enhancement. However, species-specific feed development and strict nutrient management are required to overcome current growth limitations and mitigate eutrophication risks. Levels of heavy metals (Fe, Zn, Cu, Pb, Ni, and Cd) in five commercial fish species collected from the Red Sea and Gulf of Aden, mainly Pomadasys argenteus, Aprion virescens, Valamugil sehli, Epinephelus areolatus and Thunnus tonggol were measured to assess contamination and health risks. The flame Atomic Absorption Spectrophotometry (AAS) method was adopted for measuring all selected elements. The results showed that variations in heavy metal concentrations within the muscle tissues of the examined fish were mainly attributed to the geochemical nature of beach deposits rather than anthropogenic input. All muscle samples analyzed had concentrations of Fe, Ni, Zn, Cu, Pb, and Cd below the standards reported by the National Health and Medical Research Council (NHMRC). Thus it was concluded that the investigated heavy metals do not present an environmental hazard for the present time. Cd, Ni, and Pb are harmful and cause cancer diseases.

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Published on: May 14, 2026 Pages: 1-8

Full Text PDF Full Text HTML DOI: 10.17352/ams.000051
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