Production of thailand tilapia Oreochromis niloticus, stocked at different stocking densities in small cages placed in fish farm ponds populated with the same specie and not populated

Abstract

The objective of this study was to assess the growth performance of the Thai tilapia in net cages placed in populated or not populated ponds. The study was carried out in Pindamonhangaba, São Paulo, Brazil, from February to April 2001 (summer/fall). Two 2,400 m² ponds (V₁ and V₂) were used and six 1 m³ cages (TRV₁ and TRV₂) with Thai tilapia males at densities of 200, 250 and 300 fish/m³, with one replication by the treatment, were provided for each pond. V₂ was also populated with 4,800 free male units of Thai tilapia. Initial mean length and weight were 15.90 cm and 79.60 g. After 76 days of culture, the final mean weight of the TRV₁  units was 612.5; 581.5 and 533.3 g, respectively to the employed fish densities, which was significantly higher (p<0.05) than the values exhibited by the fish from TRV₂, where only the units kept at the density of 200/m³ reached 500 g. The mean weight increase ranged from 6.0 to 7.0 g/day (TRV₁) and from 5.2 to 5.7 g/day (TRV₂ and free fish). The apparent feed conversion was around 1.0:1 for the confined fish and 1.3:1 for the free ones; survival rate was over 90% for all the treatments. The final biomass was 809.20 kg/6 m³ (V₁) and 2,444.60 kg/2,400 m² (V₂), representing a total net yield 2.7 times higher than in V₁. However, the net yield per kilogram of produced fish was a little higher for the tilapias from TRV₁ than for the units from TRV₂ and the free fish in V₂. The results indicate the feasibility of the utilization of cages in populated pond in production system.