Stocking density and tank size in the design of breed improvement programsfor body size of tilapia

Various aspects of cultural conditions were investigated in an effort to de sign an efficient selective breeding scheme for tilapia. High density cultu re has the potential of reducing confounding environmental effects associat ed with fish behavior. Body size of fry reared through 56 days was not affe cted by any of the stocking densities used (10-200 fry/l) with uniform wate r inflow. However, when water inflow was proportional to fish density, high density culture of fingerlings (18 fish/l) did appear to promote growth an d result in improved normality of the distribution of body size relative to fish stocked at lower (2 fish/l) or higher (200 fish/l) densities. Althoug h this could be interpreted as a consequence of diminished social interacti ons, a definitive conclusion could not be made in the absence of direct obs ervational data on individual fish. Mixed-model methodology was used to est imate genetic parameters for body size. Estimated heritability for body wei ght was about 0.25 for all ages from 56 to 126 days. Phenotypic and genetic correlations among body weights at various ages were positive and near uni ty. (C) 1999 Elsevier Science B.V. All rights reserved.