Zhuoying Weng

The humpback grouper (Cromileptes altivelis), an Epinephelidae species, is patchily distributed in the reef habitats of Western Pacific water. This grouper possesses a remarkably different body shape and notably low growth rate compared with closely related grouper species. For promoting further research of the grouper, in the present study, a high-quality chromosome-level genome of humpback grouper was assembled using PacBio sequencing and high-throughput chromatin conformation capture (Hi-C) technology. The assembled genome was 1.013 Gb in size with 283 contigs, of which, a total of 143 contigs with 1.011 Gb in size were correctly anchored into 24 chromosomes. Moreover, a total of 26,037 protein-coding genes were predicted, of them, 25,243 (96.95%) genes could be functionally annotated. The high-quality chromosome-level genome assembly will provide pivotal genomic information for future research of the speciation, evolution and molecular-assisted breeding in humpback groupers. In addition, phylogenetic analysis based on shared single-copy orthologues of the grouper species showed that the humpback grouper is included in the Epinephelus genus and clustered with the giant grouper in one clade with a divergence time of 9.86 Myr. In addition, based on the results of collinearity analysis, a gap in chromosome 6 of the humpback grouper was detected; the missed genes were mainly associated with immunity, substance metabolism and the MAPK signal pathway. The loss of the parts of genes involved in these biological processes might affect the disease resistance, stress tolerance and growth traits in humpback groupers. The present research will provide new insight into the evolution and origin of the humpback grouper.

This is the first genetic evaluation of hatchery-based stock enhancement of black sea bream (Acanthopagrus schlegelii) in the South China Sea after a two-year monitoring period. In this study, microsatellite DNA markers were used to calculate the contribution rate and analyze genetic changes before and after stock enhancement. Two out of one hundred and sixty nine individuals from three recaptured populations were assigned to broodstock with a contribution rate of 1.18%, revealing that the hatchery-released juvenile fish could survive in the natural environment and had a positive effect on population replenishment in wild black sea bream abundance. However, we found that the release population had the lowest genetic diversity and significant genetic differentiation from other populations. In addition, genetic diversity detected in the recaptured population was lower than that in the wild population, and their genetic differentiation reached a significant level. Our results suggested that releasing cultured black sea bream juveniles with low genetic quality might be genetically harmful for the maintenance of wild genotypes. Therefore, it is necessary to assess the genetic variation of the hatchery population before implementing a stock enhancement and establish a long-term evaluation for monitoring the genetic effect caused by releasing this fish species.

Pedigree information is necessary for the maintenance of diversity for wild and captive populations. Accurate pedigree is determined by molecular marker-based parentage analysis, which may be influenced by the polymorphism and number of markers, integrity of samples, relatedness of parents, or different analysis programs. Here, we described the first development of 208 single nucleotide polymorphisms (SNPs) and 11 microsatellites for giant grouper (Epinephelus lanceolatus) taking advantage of Genotyping-by-sequencing (GBS), and compared the power of SNPs and microsatellites for parentage and relatedness analysis, based on a mixed family composed of 4 candidate females, 4 candidate males and 289 offspring. CERVUS, PAPA and COLONY were used for mutually verification. We found that SNPs had a better potential for relatedness estimation, exclusion of non-parentage and individual identification than microsatellites, and > 98% accuracy of parentage assignment could be achieved by 100 polymorphic SNPs (MAF cut-off < 0.4) or 10 polymorphic microsatellites (mean H_o = 0.821, mean PIC = 0.651). This study provides a reference for the development of molecular markers for parentage analysis taking advantage of next-generation sequencing, and contributes to the molecular breeding, fishery management and population conservation.