Hsp70 Gene Family in Sebastiscus marmoratus: The Genome-Wide Identification and Transcriptome Analysis under Thermal Stress.

Heat shock protein 70 kDa (Hsp70) is a highly conserved heat stress protein that is important in biotic processes and responses to abiotic stress. Hsp70 genes may be important in Sebastiscus marmoratus, for it is a kind of nearshore reef fish, and habitat temperature change is more drastic during development. However, genome-wide identification and expression analysis in the Hsp70 gene family of S. marmoratus are still lacking. Here, a total of 15 Hsp70 genes in the genome of S. marmoratus are identified, and their expression patterns were investigated using transcriptomic data from thermal stress experiments. The expansion and gene duplication events of Hsp70 genes from the Hspa4, Hspa8, and Hspa12a subfamilies in S. marmoratus are revealed by phylogenetic analysis. qRT-PCR expression patterns demonstrated that seven Hsp70 genes were significantly up-regulated and none were significantly down-regulated after heat treatment. Only the hsp70 gene was significantly up-regulated after cold treatment. The selection test further showed a purifying selection on the duplicated gene pairs, suggesting that these genes underwent subfunctionalization. Our results add novel insight to aquaculture and biological research on S. marmoratus, providing important information on how Hsp70 genes are regulated in Scorpaeniformes under thermal stress.

Whole genome survey analysis and microsatellite motif identification of Sebastiscus marmoratus.

The marbled rockfish Sebastiscus marmoratus is an ecologically and economically important marine fish species distributed along the northwestern Pacific coast from Japan to the Philippines. Here, next-generation sequencing was used to generate a whole genome survey dataset to provide fundamental information of its genome and develop genome-wide microsatellite markers for S. marmoratus. The genome size of S. marmoratus was estimated as approximate 800 Mb by using K-mer analyses, and its heterozygosity ratio and repeat sequence ratio were 0.17% and 39.65%, respectively. The preliminary assembled genome was nearly 609 Mb with GC content of 41.3%, and the data were used to develop microsatellite markers. A total of 191,592 microsatellite motifs were identified. The most frequent repeat motif was dinucleotide with a frequency of 76.10%, followed by 19.63% trinucleotide, 3.91% tetranucleotide, and 0.36% pentanucleotide motifs. The AC, GAG, and ATAG repeats were the most abundant motifs of dinucleotide, trinucleotide, and tetranucleotide motifs, respectively. In summary, a wide range of candidate microsatellite markers were identified and characterized in the present study using genome survey analysis. High-quality whole genome sequence based on the "Illumina+PacBio+Hi-C" strategy is warranted for further comparative genomics and evolutionary biology studies in this species.

Effect of Water Temperature and Photoperiod on Final Oocyte Maturation in Red Marbled Rockfish, Sebastiscus tertius.

Rearing experiments were conducted using several regimes combined with different photoperiods and water temperatures to investigate the role of temperature and photoperiod as environmental cues regulating reproduction in red marbled rockfish, Sebastiscus tertius. The initial gonadosomatic index (GSI) was 1.62±0.32% and that in the 15°C control was 7.01±0.46% at the end of the experiment. The highest GSI was 9.10 ± 0.35% in the 12L:12D photoperiod-treated fish. The highest GSI at 19°C was 15.03±0.86% in the 12L:12D photoperiod treatment. The initial hepatosomatic index (HSI) was 3.09±0.72% and that in the 15°C control was 3.88 ± 0.45%. The highest HSI was 4.00 ± 0.56% in the 15L:9D treated fish. The highest HSI at 19°C was 4.05±0.63% in the 12L:12D treated fish.