Genetic parameters for fillet traits and body measurements in Nile tilapia (Oreochromis niloticus L.)

Fillet weight is an economically important trait in Nile tilapia production for the European market which asks for fish with average body weights of at least 700 g. Genetic parameters to design or optimize breeding programs for these body weights are lacking. In an earlier study we showed that high phenotypic correlations exist between body measurements and fillet weight and low phenotypic correlations exist between body measurements and fillet yield. To evaluate the potential of mass selection for fillet traits, however, genetic parameters are required. The aim of the current study was to estimate genetic parameters for body weight, fillet weight, fillet yield and body measurements. Therefore, slaughter data was collected on 1884 pedigreed Nile tilapias. Measurements of body weight, length, width, corrected (=fillet) length and head length were taken on each fish. Filleting machines were used to fillet fish and measurements of fillet weight, fillet yield and head weight were collected. Subsequently, genetic parameters were estimated. Heritabilities were 0.26 for body weight, 0.24 for fillet weight and 0.12 for fillet yield. The genetic correlation between body weight and fillet weight was 0.99 and between body weight and fillet yield 0.74. The genetic correlation between fillet weight and fillet yield was 0.81. Genetic correlations between fillet weight and body measurements were 0.89 for length, 0.70 for head length, 0.94 for width and 0.91 for corrected length. Genetic correlations between fillet yield and body measurements were 0.62 for length, 0.47 for head length, 0.98 for width and 0.60 for corrected length. The potential of mass selection aiming to improve fillet weight was evaluated by a number of selection indexes. The accuracy of a selection index including only body weight indicated that in this way almost the same amount of the selection response could be achieved compared to what hypothetical direct selection for fillet weight would. The use of only width in the selection index would result in 8.5% lower selection response than the use of body weight. We conclude that body weight is the best predictor for fillet weight compared to body measurements.