Growth performance of Thailand tilapia, Oreochromis niloticus, stocked at different quantities of net cages placed in populated ponds with the same species

Abstract

The objective of this study was to evaluate the productivity of the Thailand tilapia, Oreochromis niloticus, confined in different numbers of cages placed in populated ponds. The research was carried out in Pindamonhangaba, SP, Brazil, from February to June 2002. Two 2,400 m² ponds (V₁ and V₂) were populated with 4,800 Thailand tilapia males (13.0 cm and 48.0 g) and had 5%/day of water rate renovation and supplementary aeration. Six cages (TRV₁) were provided for pond 1 (V₁) and twelve (TRV₂) for pond 2 (V₂). Each 1 m³ cage received 250 males of Thailand tilapia (13.7 cm and 51.0 g). After 120 days of culture, the mean weight of the TRV₁ tilapias was 504.0 g, significantly higher (p < 0.05) than that exhibited by the individuals from TRV₂ and the free ones of V₁ and V₂. Significant differences (p < 0.05) were found for the values of relative condition factor among the four treatments, being the highest value for the TRV₁ tilapias. In spite of supplementary aeration, a sharp decrease in the O₂ concentration in V₂ led to high mortality, especially among the confined individuals (TRV₂) and the survival rate was 63%. In the other treatments, such rate was over 80%. Apparent feed conversion rate was 1.27:1 and 1.37:1, respectively, for the individuals from TRV₁ and TRV₂, and around 1.60:1 for the free fish. Final total biomass of the free and confined fish in V₁ was similar to that exhibited by the fish in V₂, but the net income was 30% higher than that obtained in V₂. Under the conditions of this experiment, placing six cages in a populated pond is economically viable, but the utilization of twelve cages reduced the water quality and, consequently, also the weight gain and survival rate of the fish, suggesting that the pond reached its carrying capacity.