The Pacific abalone Haliotis discus hannai is used for commercial aquaculture in Korea. We examined the transcriptome of Pacific abalone Haliotis discus hannai siblings using NGS technology to identify genes associated with high growth rates. Pacific abalones grown for 200 days post-fertilization were divided into small-, medium-, and large-size groups with mean weights of 0.26 ± 0.09 g, 1.43 ± 0.405 g, and 5.24 ± 1.09 g, respectively. RNA isolated from the soft tissues of each group was subjected to RNA sequencing. Approximately 1%–3% of the transcripts were differentially expressed in abalones, depending on the growth rate. RT-PCR was carried out on thirty four genes selected to confirm the relative differences in expression detected by RNA sequencing. Six differentially-expressed genes were identified as associated with faster growth of the Pacific abalone. These include five up-regulated genes (including one specific to females) encoding transcripts homologous to incilarin A, perlucin, transforming growth factor-beta-induced protein immunoglobulin-heavy chain 3 (ig-h3), vitelline envelope zona pellucida domain 4, and defensin, and one down-regulated gene encoding tomoregulin in large abalones. Most of the transcripts were expressed predominantly in the hepatopancreas. The genes identified in this study will lead to development of markers for identification of high-growth-rate abalones and female abalones.

Background: Prolactin (PRL) is a key hormone for osmoregulation in fish. Levels of PRL in the pituitary gland and plasma ion composition of clownfish seem to change to regulate their hydromineral balance during adaptation to waters of different salinities. In order to understand osmoregulatory mechanism and its association with growth performance and PRL in fish, the gene encoding PRL and its expression level in cinnamon clownfish Amphiprion melanopus upon acclimation to low salinity was analyzed. Results: The PRL gene of A. melanopus encoded a protein of 212 amino acid residues comprised of a putative signal peptide of 24 amino acids and a mature protein of 188 amino acids. Analysis of growth performance under different salinities of 34, 25, 15, and 10 ppt indicated that cinnamon clownfish could survive under salinities as low as 10 ppt. A higher rate of growth was observed at the lower salinities as compared to that of 34 ppt. Upon shifting the salinity of the surrounding water from 34 ppt to 15 ppt, the level of the PRL transcripts gradually increased to reach the peak level until 24 h of acclimation at 15 ppt, but decreased back as adaptation continued to 144 h. In contrast, levels of plasma Na⁺, Cl^-, and osmolality decreased at the initial stage (4–8 h) of acclimation at 15 pt but increased back as adaptation continued till 144 h. Conclusion: Cinnamon clownfish could survive under salinities as low as 10 ppt. Upon shifting the salinity of the surrounding water from 34 ppt to 15 ppt, the level of the PRL transcripts gradually increased during the initial stage of acclimation but decreased back to the normal level as adaptation continued. An opposite pattern of changes - decrease at the beginning followed by an increase - in the levels of plasma Na⁺, Cl^-, and osmolality was found upon acclimation to low salinity. The results suggest an involvement of PRL in the processes of osmoregulation and homeostasis in A. melanopus.

Genes that influence the growth of Pacific abalone (Haliotis discus hannai) may improve the productivity of the aquaculture industry. Previous research demonstrated that the differential expression of a gene encoding a C-type lectin domain-containing protein (CTLD) was associated with a faster growth in Pacific abalone. We analyzed this gene and identified an open reading frame that consisted of 145 amino acids. The sequence showed a significant homology to other genes that encode CTLDs in the genus Haliotis. Expression profiling analysis at different developmental stages and from various tissues showed that the gene was first expressed at approximately 50 days after fertilization (shell length of 2.47 ± 0.13 mm). In adult Pacific abalone, the gene was strongly expressed in the epipodium, gill, and mantle. Recombinant Pacific abalone CTLD purified from Escherichia coli exhibited antimicrobial activity against several Gram-positive bacteria (Bacillus subtilis, Streptococcus iniae, and Lactococcus garvieae) and Gram-negative bacteria (Vibrio alginolyticus and Vibrio harveyi). We also performed bacterial agglutination assays in the presence of Ca²⁺, as well as bacterial binding assays in the presence of the detergent dodecyl maltoside. Incubation with E. coli and B. subtilis cells suggested that the CTLD stimulated Ca²⁺-dependent bacterial agglutination. Our results suggest that this novel Pacific abalone CTLD is important for the pathogen recognition in the gastropod host defense mechanism.