Impact of selection for growth and stocking density on Nile tilapia production in the biofloc system

Environmentally friendly aquaculture systems such as the biofloc technology (BFT) are gaining prominence, as well as the use of genetically superior fish and better adapted strains. However, sustainable systems must be economically efficient as well. According to literature, Nile tilapia takes a longer time to reach commercial weight in BFT if compared to traditional systems, reducing profitability. A better adapted strain, with faster growth, feed efficiency and tolerance to the intensive conditions of the BFT, should be an alternative to improve the profitability of the system. This study evaluated the economic and growth performance of Nile tilapia populations from two distinct generations, the base generation (G0) and generation 5 (G5), from a genetic improvement program based on genetic selection for body weight in BFT and recirculating aquaculture system, under two different stocking densities (12.5 and 37.5 ind. & BULL; m-3) in BFT. A total of 320 male fingerlings (160 from G0 and 160 from G5) were randomly distributed in a factorial arrangement (2 x 2, four treatments) with four replicates (800 L tanks) for each treatment (16 sample units in total). The means were compared using two-way ANOVA and SNK's test (p < .05) and the confidence interval (95%) of the differences between them. The water management measures were enough to keep the water indicators within the acceptable ranges for tilapias. Survival rate was high (> 90%) for all treatments. The daily weight gain (DWG) was greater for G5 compared to G0 and resulted in a reduction of >57 days in slaughter time (750 g of harvested weight) for G5 compared to G0 and a 0.22 reduction in feed conversion ratio. The G5 promoted an average reduction of US$ 246.38 & BULL; 100 m � 3 for total operating cost and added US$ 275.97 & BULL; 100 m � 3 in operating profit compared to G0. Considering the economic analysis in relation to one ton of tilapia produced, G5 reduced the total operating cost and increased the operating profit only in the lowest stocking density. The increase in stocking density reduced the DWG for both generational groups, resulting in an increase of average time to slaughter of 43.61 days, however, 37.5 tilapia & BULL; m � 3 promoted a larger operating profit per 100 m � 3 (+ US$ 832.60) and per ton of tilapia produced (+ US$ 338.90 for G0 and + US$ 148.39 for G5). This study demonstrates the importance of using genetically improved tilapia together with an adequate stocking density management to achieve better productivity and to make economically more viable an environmentally friendly system.