Efficiency of a stand-alone Recirculating Aquaculture System for tilapia production in cold highland Kenya: a comparison with earthen pond culture

Kenya's per capita fish consumption of 4.5 kg/year is well below the global average of 20.3 kg, partly due to the unsuitability of cold highland regions for conventional pond aquaculture. This study evaluated the production efficiency of a stand-alone Recirculating Aquaculture System (RAS); the FisHub model, compared to an earthen pond under cold highland conditions in Limuru, Kenya (annual mean temperature: 19°C; altitude: 2,500 m asl). All-male Oreochromis niloticusfingerlings (25 ± 0.5 g) were cultured for 60 days in the FisHub RAS (50 m³, 120 fish/m³) and an earthen pond (300 m3, 3 fish/m2). Productivity in the FisHubwas significantly higher (13.3kg/m³ as compared to 0.8 kg/m³; Mann-Whitney U, p < 0.01), with daily growth rates of 2.2 and 0.84 g/day, and food conversion ratios of 1.0 and 2.1, respectively. Multiple linear regression identified morning dissolved oxygen(p < 0.01), morning temperature (p = 0.042), and pH (p = 0.039) as significant productivity determinants. These results demonstrate that stand-alone RAS can overcome the temperature and oxygen constraints limiting conventional aquaculture in cold highlandenvironments, offering a viable pathway to increase Kenya's domestic fish production.