Heritability of growth traits in the Asian seabass (Lates calcarifer)

Growth is an economically important trait in aquaculture.To improve growth trait of the Asian seabass(Lates calcarifer)we have been carrying out,since 2004,a selective breeding program.This study focuses on growth traits in the F2 fish generation,comprised of offspring from 23 mass crosses from 383 F_(1) brooders.Using genotyping analysis for 10 microsatellites from both brood stock and progeny we have reconstructed the pedigree of each mass-cross.For F_(2) generation at 90 days post hatch(dph),we have recorded body weight(BW)for 12,117 individuals and total length(TL),standard length(SL)and condition factor(K_(tl) and K_(sl))for 3530 individuals;and all five traits for 2136 individuals at 270 dph.At 90 dph the average BW was 46.88±20.95 g.Combining pedigree information,recorded growth traits and Restricted Maximum Likelihood method,we have estimated that the narrow sense heritability(h^(2))in F_(1) fish for BW,TL,SL,K_(tl) and K_(sl) was at,90 dph,0.12±0.03,0.11±0.03,0.10±0.03,0.20±0.04 and 0.11±0.03,respectively and,at 270 dph,0.34±0.07,0.32±0.07,0.30±0.06,0.13±0.04 and 0.11±0.04,respectively.At 90 dph the realised heritability for BW was 0.13.Comparing with F_(1) generation,the growth performance of F_(2) fish was increased by 14.4%.Heritability of growth traits will be useful for future genetic improvement programmes of the Asian seabass.

Who eats whom,when and why?Juvenile cannibalism in fish Asian seabass

While juvenile cannibalism plays an important role in the evolution of organisms in natural populations,it is a serious problem in aquaculture.A number of genetic and environmental factors result in different rates of cannibalism.Whether there is kin recognition in juvenile cannibalism in fish is poorly understood.We studied cannibalism and kinship recognition in juveniles of Asian seabass using molecular parentage analysis with polymorphic microsatellites.In the three mass crosses,under an ordinary feeding scheme without size grading,the rate of juvenile loss due to cannibalism was 1.08% per day.In the group without feeding for 24 h,2.30%±0.43% of offspring per day were lost within 24 h due to cannibalism.We detected that juveniles avoided cannibalizing their siblings when they were not hungry,whereas cannibalism among siblings increased when they were hungry.These data suggest that there is kin discrimination in fish cannibalism.Raising genetically closely related offspring in the same tanks and appropriate levels of feeding may reduce the rate of cannibalism.We hypothesized that the chemical cues for kin discrimination might be secreted by fish skins.To test this hypothesis,we analyzed gene expression profiles in the skins of juveniles under slightly and very hungry conditions using RNA sequencing and bioinformatics analysis.Genes differently expressed under slightly and very hungry conditions were identified.Among them,genes from the trypsin family were significantly downregulated under starved conditions,suggesting that they may play a role in kin discrimination.