Effects of different stocking densities on Nile tilapia performance and profitability of a biofloc system with a minimum water exchange

Abstract

The determination of an optimum stocking density should be obtained according to a complex assessment, in which growth performance, water quality, animal welfare, and production costs need to be considered. In this context, the objective of this work was to evaluate different stocking densities of Nile tilapias in biofloc technology (BFT) with minimal water renewal. Six hundred masculinized Nile tilapia juveniles with an initial average weight of 133.91 g were evaluated at four different stocking densities (18.75, 37.50, 56.25, and 75.00 fish‧m−3) and four replications, during 260 days of trial. The increase in stocking density resulted in a reduction of DO and pH. The minimum water renewal at a rate of 5%‧day−1 promoted an average reduction of settleable solids in the system of 23.75% at each discharge. The final biomass followed a quadratic regression on the stocking density, with a maximum at 72.27 fish‧m−3 or 36.86 kg‧m−3. However, the greatest daily weight gain (2.84 g‧day−1) that resulted in the highest average final body weight (842.26 g) was obtained at the lowest stocking density. We did not obtain any significant differences in body composition. The biofloc, on the other hand, had lower ash content and higher gross energy in the high stocking densities. Regarding gill morphometry, we found a greater number of branchial lesions in the highest and lowest stocking density evaluated. By an economical assessment, if the sales price is influenced by the final body weight, the reduced average harvest weight in higher stocking densities could lead to low profitability or even financial loss. Therefore, it is concluded that the use of intermediate stocking density, around 33 fish‧m−3, has higher profitability since it produces a large proportion of harvested fish that reach high body weights, and possible high selling prices, combined with desirable biomass.