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.

Inferring the invasion mechanisms of the red swamp crayfish in China using mitochondrial DNA sequences

The red swamp crayfish,Procambarus clarkii,is a native species in north-eastern Mexico and south-central USA.P.clarkii was introduced to China in 1929 and has been used as an aquaculture species in China since 1983.It currently exists in most of the provinces of China,but threatens local fish,crustaceans,aquatic plants and local freshwater ecosystems.We examined the genetic variation in partial mitochondrial ND2 gene of 831 individuals collected from 25 P.clarkii populations in 13 provinces of China to infer the expansion pathways and mechanisms.Six haplotypes were detected.All six haplotypes appeared in four populations in Nanjing and a population located near Nanjing whereas only 1–5 of the six haplotypes were present in other populations.These data suggest that the populations in Nanjing are probably the source of all other populations in China.There were no significant relationships between geographic distances and genetic distances in 25 populations,whereas significant relationship was found in four populations in Qinhuai River covering 50 km in Nanjing.These data suggest that the expansion mainly be human-mediated in large scale,and active disposal or non-anthropogenic passive dispersal might have played an important role in expansion at a smaller scale.In some places far away from Nanjing,several haplotypes existed,suggested multiple introduction events may have happened.Although aquaculture of this species could bring huge economic benefit,its potential to negatively affect native biota and entire ecosystems should not be ignored.

Genes for sexual body size dimorphism in hybrid tilapia(Oreochromis sp.x Oreochromis mossambicus)

Tilapias are important aquaculture species.Male-biased sexual size dimorphism is very common and males are preferred for aquaculture in tilapia.However,the mechanisms underlying sexual dimorphism remain to be elucidated.One hundred and thirty-six sex-biased genes,of which 23 were male-biased and 113 were femalebiased,were identified via reanalysis of a muscle transcriptome data using the latest reference genome assembly.These genes were mapped to KEGG pathways that are related to somatic cell metabolism,growth and differentiations,such as MAPK,FoxO4 and metabolism pathways as well as developmental processes responsible for skeletal muscle development.Pathways related to cell growth and proliferations such as MAPK signaling pathways are upregulated in males while pathways regulating cell division such as FoxO4 are upregulated in females.Sex-biased genes in tilapia skeletal muscle have higher evolution rates(dN/dS)compared to unbiased genes.Female-biased and male-biased genes showed 17.4%and 13.5%higher dN/dS,respectively,compared to unbiased genes.Our results suggest that some of the male and female sex-biased genes were under selection pressures.Three SNPs located in the promoter region of one sex-biased gene RASGRF1 on LG1 were associated with bodyweight differences in the hybrid tilapia.These sex-biased genes identified in this study may serve as candidate genes for future functional analysis on sexual size dimorphism and for developing DNA markers for selecting fast-growing saline tilapia in aquaculture.