Breeding for improved resistance to Edwardsiella ictaluri in striped catfish (Pangasianodon hypophthalmus): Quantitative genetic parameters.

Bacillary necrosis of Pangasius (BNP), caused by Edwardsiella ictaluri, is one of the most devastating diseases in striped catfish farming. To date, quantitative genetic inheritance of BNP resistance is not known in striped catfish Pangasianodon hypophthalmus. The main aim of this study was to estimate genetic parameters for BNP resistance in a breeding population of striped catfish undergoing four generations of selection for high growth. Specifically, the study examined whether BNP resistance is heritable to enable family selection and whether genetic improvement for enhanced BNP resistance may have detrimental effects on growth and survival rate. To test these hypotheses, 720 full- and half-sib families were challenged with E. ictaluri pathogen using injection and cohabitation methods over four years, from 2010 to 2012 and 2015. In total, the data included 398,234 animals in the pedigree, from which 18,849 animals had disease challenge test records and 39,103 siblings had growth performance. Both univariate and bivariate sire-dam linear and threshold mixed models were used to estimate (co)variance components for BNP resistance, survivals and growth traits. The estimates of heritability for the BNP resistance recorded as death or survival were low regardless of models used (0.10-0.16), whereas survival time (days post-challenge test) showed moderate heritability (0.35). The survival rate during hapa rearing had medium heritability (0.33-0.52). The genetic correlations of BNP resistance with body weight and survival were all positive (0.03-0.53), suggesting that selection of increased BNP resistance may have positive impacts on growth and survival traits, and these traits could be easily improved simultaneously in the selective breeding programme for striped catfish.

Effects of selection for fast growth on survival rate during grow-out phase in giant freshwater prawn (Macrobrachium rosenbergii).

BACKGROUND: Correlated genetic response in survival to selection for high growth has not been reported in giant freshwater prawn (GFP) (Macrobrachium rosenbergii). The main aim of this study was to measure genetic changes and estimate heritability for this character (survival rate) and its genetic associations with body traits in a GFP population selected over eight generations from 2008 to 2015. Statistical analyses were conducted on 106,696 data records, using threshold logistic mixed model. RESULTS: The estimated heritability for survival was 0.14 ± 0.04 and significant. Genetic associations of survival with body traits (weight, length and width) were weak, with the estimates of genetic correlations between the traits close to zero. Realised genetic changes in survival, calculated as the difference in estimated breeding values between the selection line and control group within the same generation, was in positive direction but the estimates were not significantly different from zero regardless of the expression unit used either in actual unit of measurement or genetic standard deviation unit. On the other hand, communal testing of stocks in the latest generation, namely G7 (2015), showed that the selection line had 18% higher survival rate than progeny of the wild prawns originated from Mekong river. This result suggests that inadvertent changes in survival occurred during domestication-selection. CONCLUSIONS: It is concluded that selection for high growth had no significant effect on survival in the present population of M. rosenbergii.