This study was conducted to investigate the effect of stocking density on the growth and survival of Oreochromis andersonii Kafue bream nursed over winter in tarpaulin lined concrete ponds (35 m3). The aim was to help find mitigation measures against adverse effects of the cold season (May to August) on tilapia hatchery and grow-out operations in Zambia.
Mono sex tilapia fry (2g) were cultured in hapas (1m3) for a period of 10 weeks. Five stocking densities of 25 (T1), 50 (T2), 100 (T3), 200 (T4) and 400 (T5) fry/hapa with three replicates were used. Fry were fed twice daily, except on weekends, with a commercial feed containing 45% protein at 5% of total biomass. To preserve water temperatures, the ponds were covered with a transparent polyethylene sheet (200µm) and water exchange was done once a week.
Temperature was maintained at an average of 23.5±1.74°C, which was 6.5 degrees higher than the average winter temperatures of open ponds. After 10 weeks, there were no significant differences (p<0.05) between the weights of fish, fry survival rates and Specific Growth Rate (SGR) for all treatments (Table 1).
These findings could mean O. andersonii fry adapt well to overcrowding under favorable water temperatures, well maintained water quality and an appropriate feeding regime.
We conclude that stocking density had no significant effect on growth and survival of O. andersonii. However, the current study did not reach the carrying capacity, hence we are not able to state an optimum stocking density of fry in the hapa system.
We recommend culture of fry in hapas at a high density (400 fry/m3) in covered concrete ponds to help overcome the challenges that come with nursing of fry during winter. This could also be a good way to ensure an early onset of the grow–out season by providing ready to stock fingerlings immediately after the winter season. We recommend further studies to establish the optimum stocking density of tilapia fry in the hapas.
Key words: O. andersonii, hapas, stocking density, winter