Advanced nursing of mixed-sex and mono-sex tilapia (Oreochromis niloticus) fry, and its impact on subsequent growth in fertilized ponds

Abstract

A 168-day grow-out trial was conducted using mono-sex and mixed-sex tilapia (Oreochromis niloticus) fries nursed for 2, 4 or 6 months to investigate the comparative effects of advanced nursing on subsequent growth and survival. Fingerlings were kept in nylon hapas and fed at 5% biomass day−1 during advanced nursing (4 or 6 months) before stocking at 3 fishes m−2 in 18 fertilized earthen ponds (200 m2). Survival rates of mono-sex and mixed-sex tilapia during advanced nursing were comparable (greater than 70%). During the subsequent grow-out phase, survival of both mono-sex and mixed-sex tilapia increased linearly with duration of nursing (y=36.12+4.93x, n=9, r2=0.56, P less than 0.05 and y=21.38+8.45x, n=9, P less than 0.05), respectively. Prolonged nursing increased the level and consistency of survival in both mixed- and mono-sex stocks during subsequent grow-out. Overall, mono-sex fishes reached a larger final individual size (128.8±6.8 g) than mixed-sex (112.7±14.6, P less than 0.05). This effect was most pronounced for the 6-month-old seed of which mixed-sex reproduced early in the production cycle. However, survival, daily weight gain, specific growth rate and net fish yield were not significantly different (P greater than 0.05) between mono-sex and mixed-sex tilapia. A decreasing trend in daily weight gain, specific growth rate and individual harvested size of the stocked fishes was observed with increase in nursing period in mixed-sex tilapia due to reproduction. It was concluded that the duration of nursing was critical to producing homogeneous mixed-sex fish, and that prolonged nursing may be a useful strategy for production of mono-sex tilapias.