Breeding Asian seabass to increase survival against big belly disease and growth

Abstract

Asian seabass (Lates calcarifer) is an important foodfish species. It has been cultured in Singapore since the 1980s. A selective breeding program to improve growth, meat quality and disease resistance has been ongoing in Singapore since 2004. In 2012, outbreaks of the big belly disease (BBD) occurred in two batches of offspring generated by a mass-cross among F1 brooders in a hatchery. After the outbreaks, only 437 survived in 6000 F2 juveniles. Molecular parentage analysis with 10 microsatellites revealed that four parents (F1) produced high percentage of offspring that survived the BBD outbreaks. Eighty-two BBD survivor offspring (F2) were selected based on their growth performance at 90 days post hatch (dph), family origin and allelic diversity. They were used as brooders to generate F3. In a period of five years, these F2 brooders produced six batches of offspring, where no outbreak of BBD occurred. In the same period, outbreaks of BBD occurred in 4 out of 18 batches produced by F2 brooders selected for growth, with mortality rates ranging from 85.1% to 95.4%. In F3, the average body weight (57.1 ± 1.09 g, n = 3068) of the line for BBD survival was slightly lower than that (60.6 ± 2.29 g, n = 4280) of the line for growth at 90 dph. In both lines, the body weight of F3 was much higher than that (46.90 ± 0.19 g, n = 12117) of F2. The genetic diversity in the line for BBD survival (F3) was much lower than that in F3 line for growth due to small founder population. These data indicate that the selection of BBD survival during BBD outbreaks using molecular parentage analysis is effective to reduce BBD outbreaks. Avoiding further reduction of genetic diversity is essential in the line selected for increased survival against BBD.