Estimates of phenotypic and genetic parameters for carcass traits in Nile Tilapia selected for fast growth in low-input conditions

Nile tilapia is sold as either un-gutted or gutted whole carcasses, or as depending on geographical location. In whichever state the is sold, meat yield is an important consideration. Although carcass traits are of economic importance, only a few estimates of phenotypic and genetic correlations have been carried out in tilapia selective breeding programs. A selection program for fast growth in low-input conditions is being carried out at the WorldCenter, Abbassa, Egypt. To evaluate the effect of selection for body weight on other body traits, we estimated heritability and phenotypic and genetic correlations between traits. Fish consisted of and second generation of selection for fast growth in low-input conditions. Fry production involved single-pair mating of each male with two females. At least 60 fry from each full-sib family were reared separately in 2 x 3 m hapas for 1-3 months after which 25 fry per family were tagged. Fish were then grown in two 1000 m2 ponds in which 50kg-1ha-1day chicken manure was applied. After 6-9 months of growth, a total of 2521 were measured for un-gutted and gutted body weight, body length, body thickness and body depth. Dressing percentage was calculated as the ratio between gutted weight (x100) and un-gutted body weight. The heritability of each trait was estimated. Furthermore, phenotypic and genetic correlations between body measurements and gutted weight and dressing percentage were recorded. Results indicate that gutted and un-gutted body weights and body depth are signiinby sex of the High heritability was recorded for un-gutted body weight (0.55 0.08, heritability standard error), head length (0.6 0.08), body depth (0.51 0.08) and body thickness (0.43 0.08). However, gutted weight, head width and dressing percentage heritability estimates were lower (0.12 0.06, 0.26and 0.18 0.06, respectively). There was high genetic and phenotypic correlation between gutted and un-gutted body weight with other traits in both years. In year two the correlation between dressing percentage and gutted weight was remarkably improved (from 0.18 to 0.52). Highest genetic correlation was recorded between gutted weight and body thickness (0.87 0.11) and standard length (0.87 0.06). Similarly, the genetic correlation between dressing percentage and body thickness and standard length were relatively high (0.38 0.27 and 0.26 0.37 respectively) indicating that body thickness can be used together with un-gutted body weight to predict and select for meat yield in tilapia.