Assessment of a long-term selective breeding program for giant freshwater prawn Macrobrachium rosenbergii since 2007

Effects of long term selection for improved growth on traits of commercial interest are generally not well documented in aquaculture species, specifically in giant freshwater prawn (GFP) Macrobrachium rosenbergii. The present study analysed a total of 106,756 data records collected from a pedigreed GFP population over nine years (2007–2015) or nine generations (including base population) to evaluate genetic progress achieved for body weight and to examine correlated genetic changes in measurements of body dimensions (carapace length, abdominal length, carapace width and abdominal width), as well as fitness related traits (early maturity, EM and small blue claw male, SM). Linear mixed model fitting the random effects of individual prawn and common full-sib groups and the fixed effects of generation, line, pond by generation subclass, morphotypes for each sex and a linear covariate of grow-out day was used to analyse growth-related traits, whereas threshold logistic animal model was applied to binary data (EM and SM). The heritabilities were moderate for body weight and measurements of body dimensions (10 to 60%), but the estimates for EM and SM were low (0.13 ± 0.06 and 0.08 ± 0.01, respectively). The proportion of variance explained by the common full-sib effects was only 5–7% for measurements of body traits (weight and body dimensions). Genetic correlations among body traits were high and positive (0.93–0.97). These body traits however showed negative (i.e. favourable) genetic correlations with both EM and SM. Direct genetic gain for body weight and correlated changes in measurements of body dimensions and fitness related traits (EM and SM) were measured as differences in estimated breeding values (EBVs) between the selection line and control group within the same generation. The accumulative genetic gain in body weight after eight generations was 56%, averaging 7% per generation. Selection for high growth, however, did not have detrimental effects on measures of body dimensions and fitness related traits (i.e. EM and SM). In comparison to one of the founder stocks collected from Mekong river, the selection line had 50% greater body weight under the same testing environment in the latest generation 2015. Our findings provide information to refine the current breeding program to simultaneously improve traits of commercial interest in this important aquaculture species M. rosenbergii.