Genetic parameters of resistance to acute hepatopancreatic necrosis disease (AHPND) caused by<i> Vibrio</i><i> parahaemolyticus</i> and their genetic correlations with growth traits in an Ecuadorian<i> Penaeus</i><i> vannamei</i> population

Abstract

Infections with strains of Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (VPAHPND) in Penaeus vannamei have not yet caused high levels of mortality in Ecuador like those reported in Asia; however, target animals resistant to VPAHPND are a goal for industrial farmers. The implementation of breeding programs to produce fast-growing and disease-resistant shrimp would be a key to addressing the expected situation. The main objective of this study was to estimate heritabilities and genetic correlations for VPAHPND resistance and growth traits in an Ecuadorian population cultured under industrial conditions. A total of 3345 animals from 155 sibling families of the PMG-BIOGEMAR (c) genetic breeding program were individually tagged, measured for initial length and weight (only for Test-1), and tested for VPAHPND in two trials: Test-1 at a concentration of 2 x 10(5) CFU/ml and infection by immersion and Test-2 at a concentration of 2 x 10(8) CFU/g and by oral infection. After 72 h, all shrimp were analysed for final weight and length, survival, and infection levels by Ct values (qPCR) of the pirA and pirB genes. Genetic parameters of growth and resistance traits were obtained using two statistical models: Linear and Threshold models. Heritabilities were medium (0.16-0.31) for growth and low (<0.09) for infection-level traits, by both methods and in both tests. In the case of survival, the heritability was low using the Linear model (0.04), and medium (0.22 and 0.26) with the Threshold model, in Test-1 and Test-2, respectively. However, the genetic correlations found between growth and survival traits were high and positive (>0.55) with both methodologies in Test-1 and low-medium and positive in Test-2 using Threshold model. The results suggest that genetic selection for growth in P. vannamei has a positive effect on resistance to AHPND. Furthermore, the genetic selection for growth over time in this Ecuadorian population may have induced possible resistance or tolerance to the disease.