Heterogeneous growth fingerlings of the Nile tilapia Oreochromis niloticus: effects of density and initial size variability.

In this study, the effect of initial heterogeneity of weight and density on heterogeneous growth (HetG) evaluated by the coefficient of the variation of weight in the young Nile tilapia Oreochromis niloticus of the territorial species was tested. Fish were maintained in a glass aquarium (8 and 2 L of water) with two levels of initial heterogeneity of weight: low and high, under two density conditions: low and high, thus constituting four conditions (six replications for each). Initially, the weights of the animals were taken after 8, 16, 22 and 30 days (end of experiment). The results, evaluated by the non-parametric test of Kruskal- Wallis, demonstrated that in the groups where the animals were stored under high initial HetG, there was a reduction of the same and that in the groups where the animals were stored under high density, there was exacerbation or maintained high values of HetG. High density in association with high initial heterogeneity caused more exacerbation of HetG in such a way that the density appeared to be a determining factor for exacerbation or the maintenance of high values of HetG, whereas the initial heterogeneity of the weight could be a secondary factor.