An on-farm study was conducted in Chingale area in Zomba, Southern Malawi to assess the growth of three tilapia fish species in earthen ponds of different sizes and water depths. The experiment was laid out in a factorial design of 200 and 400 m2 pond sizes, 0.8 and 1.2 m pond water depths, and fish species: Oreochromis karongae, Oreochromis shiranus and Tilapia rendalli, replicated thrice among randomly selected farmers. Ponds were fertilized monthly with fresh chicken manure at an application rate of 1 ton/ha and fish were fed on maize bran as a supplement at 5% body weight. Fish were sampled and weighed every four weeks over 6 months. O. karongae attained the highest weight gain (65.75 g) in smaller ponds (200 m2) translating into an overall higher gross yield of 2.91 tons/ha/year (P<0.05). Overall mean weight gain for O. shiranus (49.70 g) and O. karongae (43.87 g) was not significantly different in 400 m2 (P>0.05). Fish in deeper ponds had a significantly higher overall mean final weight (52.26 g) (P<0.05). T. rendalli exhibited the lowest average daily weight gain (0.27) especially in 200 m2 ponds, but had the highest specific growth rate (1.65%) while overall, O. karongae was the most advanced of the three tilapia species in terms of growth. Findings from this study suggest that for small-commercial fish farmers, smaller but deeper ponds produce better fish production results, hence should be adopted.
Key words: Tilapia, pond water depth, pond size, weight gain.
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