Genetic parameters for tolerance to gill-associated virus under challenge-test conditions in the black tiger shrimp (Penaeus monodon)

Diseases in shrimp aquaculture cause significant economic losses, particularly those caused by viruses. Genetic improvement of disease tolerance through selective breeding can be an important tool for managing the risk of disease in shrimp farming as long as the trait has a genetic basis (i.e. heritable) and is able to be accurately and reliably measured. This study presents the first estimates of genetic variation associated with tolerance to gill-associated virus (GAV) in Penaeus monodon using a unique controlled challenge WA design. Shrimp families (n = 72) were communally spawned and reared prior to replicated communal challenge testing when they reached an average size of similar to 8 g. Pedigree determination was carried out using genotyping and shrimp were challenged by intramuscular injection with a weight standardised dose of GAV. Daily mortality data were collected over 15 days from 1717 individuals and GAV infection load was measured on the challenge WA survivors (n = 963). Overall mortality after 15 days was 35.5% and ranged from 0 to 71% among families. Heritability estimates for mortality were 0.11 +/- 0.03 using a binomial model and 0.14 (standard error not estimated) using Cox's proportional hazards model. The estimated heritability for GAV infection load was 0.21 +/- 0.07. The genetic correlation between mortality and GAV infection load was not significantly different from zero, r(g) = 0.30 +/- 0.23, suggesting that the two traits may be genetically independent, at least in the way they were measured in this study. Results from this study suggest a low but significant genetic basis for GAV tolerance in P. monodon and that selection may be a viable option to manage GAV-related disease. The study also demonstrated, for the first time in shrimp, communal-based spawning and rearing can be used for large-scale genetic analysis of disease tolerance, eliminating the need for single family rearing tanks and associated confounding environmental effects.