Modelling of fillet traits based on body measurements in three Nile tilapia strains (Oreochromis niloticus L.)

In Nile tilapia, breeding programs focus mainly on growth, and information on genetic improvement of fillet yield is scarce. In this study, slaughter data were collected on 1215 tilapia and used to analyze the relationship between body measurements and fillet weight and fillet yield. Fish were obtained from three different origins/strains, and raised in a commercial farm in the Netherlands in closed recirculation systems until a final mean weight of 700 g. Body weight, length, height, width and corrected (= fillet) length were taken prior to slaughter, and used to predict fillet weight and fillet yield using linear regression models. Average fillet yield was 35.7% with large differences between strains (range 34.4-38%). There was a strong almost linear relationship between body measurements and fillet weight, but relationships with fillet yield were weak. R-2 of the regression model for fillet weight was 0.95 and the correlation between observed and predicted values of fillet weight 0.98. The effect of strain/origin was significant for each body measurement. The effect of sex and strain x sex was significant for length and corrected (= fillet) length. The fillet yield model explained 15% of the observed variance; the correlation between observed and predicted fillet yield was 0.38, but there were large differences within strains. We conclude that in Nile tilapia, predicting fillet yield based on body measurements is possible, but correlations can be improved if more accurate methods for measuring body width become available. (C) 2004 Elsevier B.V. All rights reserved.