Estimation of genetic parameters for resistance to Aeromonas hydrophila in blunt snout bream (Megalobrama amblycephala)

Bacterial hemorrhagic disease caused by Aeromonas hydrophila is one of the harmful bacterial diseases for aquaculture. The aim of this study was to evaluate the genetic parameters for resistance to A. hydrophila in blunt snout bream Megalobrama amblycephala. A total of 834 individuals at one-year old from 27 families were experimentally infected with A. hydrophila. During five days duration of the challenge test, deaths peaked at the second day after infection and average mortality over the whole population was 83.93% (family averages ranging from 97.22% to 22.22%). The heritability of A. hydrophila resistance (dead or alive at peak mortality, day 2, under an animal model) under cross-sectional linear (LIN), cross-sectional threshold models (THRp and THRI) was quite different, ranging from zero to 0.33. Compared with the phenotypic correlation coefficient, the genetic correlation coefficient between disease resistance and growth related traits, was relatively high for all genetic parameters. Genetic correlations of resistance to A. hydrophila with body height (0.63), body length (0.65) and body weight (0.60) were significant (P < 0.01) and positive; however, correlations of resistance with sex was non-significant (P > 0.05). These results provide the first report for heritability of resistance to A. hydrophila in M. amblycephala, and correlation with three growth related traits (body height, body length and body weight) could efficiently facilitate indirect selection of M. amblycephala with high A. hydrophila resistance.