Genetic and environmental factors affecting growth of Nile tilapia (Oreochromis niloticus) juveniles:: Modelling spatial correlations between hapas

The aim of this study was to quantify the environmental and genetic effects on early growth of Nile tilapia, Oreochromis niloticus, in papa-in-earthen pond systems. In a pilot study, we grew swim-up fry with or without supplementary feed in hapas suspended in fertilized ponds at 5, 10, 15, and 20 fry/m(2) densities. In the main experiment, we reared swim-up fry from 25 full-sib families separately for 42 days at 15 fry/m2 density in hapas suspended in two earthen ponds. Hapas were arranged in two column arrays along the sides of the ponds. Ponds were fertilized daily with chicken manure. In addition, fry in one column in each pond were fed twice daily on 40% protein pelleted feed. Results from the pilot study indicated significant effects of stocking density and treatment. In the main experiment, the dietary treatment effect was not significant but there were large differences in growth between ponds. Mean body weight at 42 days was 1.7 g in pond A and 0.4 g in pond B. Fry heritability (h(2)) of 42-day fry body weight estimated from the whole data set using a univariate model was 0.01 +/- 0.06. The bivariate heritability estimates were 0.59 +/- 0.19 in pond A and 0.05 +/- 0.11 in pond B. The common environmental/hapa (c(2)) effects were 0.14 +/- 0.06 and 0.29 +/- 0.07 in respective ponds. We found significant positive spatial autocorrelation (P=0.02) indicating resemblance in growth of fry in neighboring hapas. Analysis of environmental variables showed that the two ponds differed significantly in dissolved oxygen. The low genetic correlation (r(g)=-0.27 +/- 0.69) between body weights of fry in both ponds therefore might suggest genotype by environment interactions for tolerance to low dissolved oxygen in Nile tilapia juveniles. (c) 2005 Elsevier B.V. All rights reserved.