Genetic parameters of Gill-associated virus infection and body weight under commercial conditions in black tiger shrimp, Penaeus monodon

Abstract Selective breeding to improve performance of growth and increase disease resistance is becoming commonplace within shrimp aquaculture. Whilst estimated breeding values (EBV) for growth can be evaluated easily in on-farm trials, EBVs for disease resistance are usually obtained from controlled laboratory challenges and may not be indicative of natural infection and resistance in a commercial setting. If they are not the same trait, this will result in a low genetic correlation between the traits and application of EBVs derived from the laboratory challenge will lead to overall slow genetic progress for improved disease resistance in on-farm conditions. There is a need for alternative measures of predicting disease resistance based on performance in farm environments. Two such estimates may be viral infection status (presence/absence) and load of farm reared shrimp. This study presents genetic parameter estimates of Gill-Associated Virus (GAV) infection (viral infection presence and viral loading) and body weight traits from Penaeus monodon reared under commercial farm conditions. Body weight and GAV infection traits were assessed by sampling ~2000 shrimp from 80 full-sib families from two replicate commercial ponds. In addition, the Pearson correlation of EBVs of pond-reared shrimp with those of siblings derived from communal laboratory GAV challenge tests (intramuscular injection of standard doses of virus) were calculated to establish if prediction of genetic merit in controlled trials would be similar to disease resistance seen on-farm. Heritability under commercial farm conditions for GAV infection status was 0.06 ± 0.03 (percent GAV positive 45.5%) and infection load 0.21 ± 0.10 (mean GAV infection load 3.11 ± 1.14 log10 GAV copies μg−1 TNA) and for body weight h2 = 0.38 ± 0.07. A high genetic correlation was observed among the two on-farm GAV infection traits (rg = 0.90 ± 0.24), whereas the genetic correlation between the two GAV infection traits and body weight on-farm were positive although weak (rg = 0.26 ± 0.25; 0.36 ± 0.26). No significant correlation was found for EBVs of GAV infection (infection status and load) on-farm and GAV-induced mortality or viral load under laboratory challenge testing (REBV ranged from −0.06 ± 0.14 to −0.27 ± 0.15). Additionally, there was no correlation of EBVs between body weight of shrimp on-farm and GAV-induced disease under controlled challenge. In conclusion, measures of GAV infection from shrimp on-farm and GAV induced mortality measured under controlled challenge conditions may represent different genetic traits, at least when mortality is measured using an ‘unnatural’ challenge method and when no apparent disease outbreak occurs on farm.