Estimates of heritability and genetic correlation for body length and resistance to fish pasteurellosis in the gilthead sea bream (Sparus aurata L.)

Fish pasteurellosis is an infectious disease that affects several fish species living in marine temperate waters. Its causative agent is the Gram-negative bacterium Photobacterium damselae subsp. piscicida (Phdp). Fish pasteurellosis represents a serious health problem for the majority of intensive sea bream hatcheries, with 90-100% mortality during disease outbreaks. Larvae and juveniles are the most susceptible stages. A potential strategy to prevent fish pasteurellosis is to select for animals that are genetically resistant to it. The aim of this work was to evaluate the genetic variation of disease resistance and growth in the gilthead sea bream (Sparus aurata L.). An experimental population, approximately 3500 animals originating from mass spawning of four broodstocks, was experimentally infected with a highly virulent strain of Phdp. Mortality was monitored daily for 19 days. Upon completion of the challenge experiment, genetic profiles at nine microsatellite loci were obtained for 1753 animals and for all (256) broodstock fish, for parentage assignment. A subset of families defined by means of genetic analysis was used to calculate heritability for survival to infection. For body length (measured post-mortem), heritability was 0.38 +/- 0.07. The heritability for disease resistance varied depending on how resistance was defined. Heritability was 0.12 +/- 0.04 for days of survival post challenge, defined as a continuous trait. while it ranged from 0.45 +/- 0.04 to 0.18 +/- 0.08 for the binary trait dead/alive at a specific day. The genetic correlation between body length and survival was positive and significant (r = 0.61 +/- 0.16). These results confirm the existence of genetic variation for growth and resistance against Phpd and highlight also the potential for selective breeding programs to improve these traits.