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

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 m). Survival rates of mono-sex and mixed-sex tilapia during advanced nursing were comparable (>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, r = 0.56, P < 0.05 and y = 21.38 + 8.45x, n = 9, P< 0.05), respectively. Prolonged nursing increased the level and consistency of survival in both mixedand mono-sex stocks during subsequent grow-out. Overall, mono-sex fishes reached a larger final individual size (128.8F 6.8 g) than mixed-sex (112.7F 14.6, P< 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>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 0044-8486/03/$ see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0044-8486(03)00008-5 * Corresponding author. Institute of Aquaculture, University of Stirling, Scotland FK9 4LA, UK. Tel.: +441786-46923; fax: +44-1786-472133. E-mail address: [email protected] (D.C. Little). www.elsevier.com/locate/aqua-online Aquaculture 221 (2003) 265–276 homogeneous mixed-sex fish, and that prolonged nursing may be a useful strategy for production of mono-sex tilapias. D 2003 Elsevier Science B.V. All rights reserved.