Black Rockfish Sebastes Schlegelii Research Articles

Evaluation of starvation status in the early developmental stages of black rockfish (Sebastes schlegelii) based on morphological and histological characteristics.

Assessing the nutritional status and identifying major causes of mortality in larvae experiencing varying degrees of starvation are crucial for establishing appropriate feeding protocols and enhancing the welfare of hatchery-reared fish. The black rockfish Sebastes schlegelii is an important species in aquaculture and stock enhancement efforts in China, Japan, and Korea. This study aimed to identify optimal diagnostic morphometric indicators of starvation in newly hatched (0-6 days post-hatch, DPH) and postlarval stages (27-37 DPH) of this valuable fish species through histological analyses. Our findings revealed that certain morphometric parameters, including body length, the ratios of eye diameter to head height, body height to body length, and abdomen height to body height, exhibit sensitivity to starvation during both larval and postlarval stages. Particularly, the ratios of body height to body length and abdomen height to body height emerged as the most sensitive morphometric indicators of starvation. Histological examinations of the digestive system revealed rapid alterations in the morphology of hepatic parenchymal cells, accompanied by a significant decrease in the number of lipid cells in the liver during episodes of food deprivation. Starvation induced cellular degeneration in the digestive organs, manifested by reduced heights of epithelial cells and mucosal layers in the intestine, oesophagus, and stomach, along with degeneration and separation of muscle fibers. Among these variables, the height of the intestinal submucosa and muscle layer emerged as the most sensitive indicators reflecting nutritional conditions in newly hatched larvae. In contrast, the height of intestinal striated borders and mucosal folds proved to be the most sensitive indicators in the postlarval stage. Furthermore, the height of intestinal epithelial cells and the number of lipid vacuoles in enterocytes exhibited high sensitivity to food deprivation in both newly hatched larvae and postlarvae. These findings underscore the varying resilience of fish to starvation during different developmental phases and highlight the utility of morphological sensitivity characteristics as reliable diagnostic indices for assessing nutritional status in relation to starvation or suboptimal feeding during the early developmental stages of black rockfish in hatchery-reared processes.

Population genetics analysis of the black rockfish Sebastes schlegelii in Northern China based on 2b-RAD simplified genome sequencing

The black rockfish Sebastes schlegelii is an important fishery species in Japan, South Korea, and China. Overfishing has severely depleted the natural resources of S. schlegelii in recent years, leading to the initiation of programs aimed at enhancing fish stock. However, the genetic structure of northern populations remains elusive, posing challenges in collecting and preserving germplasm resources. In this study, a total of 191 S. schlegelii individuals from seven populations, including one cultured population (Changdao: CDYZ) and six wild populations (Lianyungang: LYG; Qingdao: QD; Weihai: WH; Changdao: CDYS; Beidaihe: BDH) sequenced by 2b-RAD method and their population genetics was analyzed using 27,064 SNPs obtained. The results indicated low genetic diversity in both wild and cultured populations (PIC < 0.25, Ho: 0.174-0.273, He: 0.173-0.234), with the cultured population exhibiting higher diversity than the wild ones. Moderate genetic differentiation existed between the cultured population and six wild populations (0.05 < Fst < 0.25). However, the genetic differentiation was lower among the other wild populations (Fst < 0.05). The analyses of population genetic structure indicated that the wild populations clustered together first and finally with the cultured population CDYZ, which clustered separately except for one individual. Therefore, scientific breeding programs and germplasm conservation can be important in stabilizing genetic structure. In addition, gene flow among the seven populations was high (Nm > 1). This study provides a theoretical basis for conserving and rationalizing germplasm resources for S. schlegelii.

Effects of Two Environmental Enrichment Methods on Cognitive Ability and Growth Performance of Juvenile Black Rockfish Sebastes schlegelii.

A widely used approach to restoring marine fishery resources is stock enhancement using hatchery-reared fish. However, artificial rearing environments, which are often lacking in enrichment, may negatively affect the cognition, welfare, and adaptive capacity to new environments of juvenile fish, thereby leading to low post-release survival rates. This study examined the effects of habitat and social enrichment on the growth performance and cognitive ability of Sebastes schlegelii. Following seven weeks of environmental enrichment, a T-maze experiment was conducted, and the telencephalon and visceral mass of the fish were sampled to measure the growth (growth hormone: GH; insulin-like growth factor-1: IGF-1; and somatostatin: SS) and cognitive abilities (brain-derived neurotrophic factor: BDNF; and nerve growth factor: NGF)-related indicator levels. The results indicated that, although the final body length, final body weight, and specific growth rate of both enrichment groups were lower than those of the control group, both methods of enrichment had a positive impact on growth-related factors (increased GH, increased IGF-1, and decreased SS). The enrichment groups demonstrated a stronger learning ability in the T-maze test, and the levels of BDNF and NGF in the telencephalon were significantly higher in the enrichment groups than those in the control group. Additionally, there was a significant interaction between the two enrichment methods on the NGF level. This study confirms that a more complex and enriching environment is beneficial for cultivating the cognitive abilities of cultured juvenile S. schlegelii, and the result can provide a reference for the improvement of the stock enhancement of this species.

Hepatic transcriptomic analysis reveals that Hif1α/ldha signal is involved in the regulation of hypoxia stress in black rockfish Sebastes schlegelii

Hypoxia has become a common problem for aquatic organisms due to the interaction of global climate change and human activity. Black rockfish inhabits rocky reefs in waters of Japan, Korea and China, whereas the limited hypoxia tolerance leads to mass mortality and great economic loss. In this study, high-throughput RNA-seq for transcriptomic analysis was used to investigate the hepatic response in black rockfish under hypoxia (critical oxygen tension, Pcrit; loss of equilibrium, LOE) and reoxygenation (recover normal dissolved oxygen 24 h, R24) to explore the mechanisms underlying hypoxia tolerance and adaptation. A total of 573,040,410 clean reads and 299 differentially expressed genes (DEGs) in total were obtained during hypoxia and reoxygenation. GO annotation and Kyoto Encyclopedia of Genes and Genomes analysis demonstrated that the DEGs are mainly enriched in the biochemical metabolic pathways and HIF-1 signaling pathways. Transcriptomic analysis also identified 18 DEGs associated with HIF-1 signaling pathway (hif1α, tf, epo, hmox, gult1, mknk2, ldha, pfkfb3, hkdc, aldoa) and biological process (hif2α, apoeb, bcl6, mr1, errfi1, slc38a4, igfbp1a, ap4m1) as further validated by quantitative real-time PCR. Moreover, hif1α was positively or negatively correlated with glucose (ldha, pfkfb3, hkdc, aldoa) and lipid (apoeb) metabolism-related genes. The mRNA level of hif1α was significantly up-regulated under acute hypoxia stress and obtained the higher values than hif2α. Meanwhile, hif1α recognized the hypoxia response element located in the promoter of ldha and directly bound to the promoter to transactivate ldha expression. These results indicated that black rockfish may mainly utilize glycolysis to maintain homeostasis, and hif1α facilities hypoxia tolerance by modulating ldha expression.

Hypoxia stress induces hepatic antioxidant activity and apoptosis, but stimulates immune response and immune-related gene expression in black rockfish Sebastes schlegelii

Dissolved oxygen concentrations both in the open ocean and coast have been declining due to the interaction of global climate change and human activity. Fish have evolved different adaptative strategies to cope with possibly damage induced by hypoxic environments. Black rockfish as important economic fish widely reared in the offshore sea cage, whereas related physiological response subject to hypoxia stress remained unclear. In this study, hepatic anti-oxidant enzymes (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GSH-Px]), aminotransferase (AST) and alanine aminotransferase (ALT) activities, lipid peroxidation (LPO), malondialdehyde (MDA) and glutathione (GSH) content, immunological parameters and the expression of apoptosis (bax, bcl2, p53, caspase3, xiap) and immune-related genes (c3, il-1β, ccl25, saa, hap, isg15) of black rockfish were determined during hypoxia and reoxygenation to illustrate the underlying defense response mechanisms. Results showed that hypoxia stress remarkably increased hepatic LPO and MDA content, AST and ALT activity and proportion of pyknotic nucleus. Hepatic SOD, CAT and GSH-Px activity manifested similar results, whereas GSH levels significantly decreased under hypoxia stress. The apoptosis rate of hepatocyte increased during hypoxia stress and reoxygenation. Meanwhile, p53, caspase3, bax and xiap mRNAs and bax/bcl2 rations were significantly up-regulated under hypoxia stress. However, bcl2 mRNA was significantly down-regulated. Interestingly, hypoxia stress significantly increased NBT-positive cell percent, phagocytic index, respiratory burst and ACH50 activity, and lysozyme activity. The mRNA levels of c3, ilβ, ccl25, saa, hap and isg15 were significantly up-regulated in the liver, spleen and head-kidney under hypoxia stress. The above parameters recovered to normal status after reoxygenation for 24 h Thus, hypoxia stress impairs hepatic antioxidant capacity, induces oxidative damage and apoptosis via the xiap-p53-bax-bcl2 and the caspase-dependent pathways, but enhances host immunity by regulating nonspecific immune indices and related genes expression to maintain homeostasis in black rockfish. These findings will help fully understand the hypoxia tolerance mechanisms of black rockfish and provide more data for offshore open ocean farming.

Hematological varieties, histological changes, and immune responses in the early stage of infection with Vibrio parahaemolyticus in Black rockfish Sebastes schlegelii

Hematological varieties, histological changes, and immune responses in the early stage of infection with Vibrio parahaemolyticus in Black rockfish Sebastes schlegelii

Effects of Stocking Density on Stress, Hematological Responses, and Growth of Black Rockfish Sebastes schlegelii.

The objective of the current study was to evaluate the effect of stocking density on juvenile Black Rockfish Sebastes schlegelii (average weight = 12 g) in terms of stress, hematological responses, and growth performance during a 4-month growth trial in a flow-through system. The initial stocking densities were 1.3 kg/m3 (low), 1.8 kg/m3 (medium), and 2.3 kg/m3 (high), and the final densities were 4.9 kg/m3 (low), 5.6 kg/m3 (medium), and 6.3 kg/m3 (high). At the end of the trial, the high stocking density significantly affected growth characteristics, levels of growth hormone and insulin-like growth factor 1, and hematological indices (hematocrit, red blood cell count, and hemoglobin level) compared to the medium and low stocking densities. The plasma cortisol and immunoglobulin-M levels were significantly higher at the high density than at the other two densities. Taken together, while the low and medium stocking densities (final densities of up to 5.6 kg/m3 ) did not affect stress and hematological indices or growth, the high stocking density (final density of 6.3 kg/m3 ) significantly impacted those variables, which suggests an allostatic load at that density. Thus, the use of a final stocking density less than 6.3 kg/m3 should be considered to avoid compromising the stress and health condition and growth of Black Rockfish at this size and temperature range.

Comparative transcriptomic analysis of gonadal development and renewal in the ovoviviparous black rockfish (Sebastes schlegelii)

BackgroundThe black rockfish (Sebastes schlegelii) has an ovoviviparous reproductive pattern and long-term sperm storage, resulting in asynchronous gonadal development between the sexes. However, the comprehensive understanding of gonadal development in black rockfish has not yet been achieved. Here, we studied gonadal development and germ cell renewal using histology and RNA-seq.ResultsIn this study, RNA-seq was performed on testes and ovaries to characterize key pathways and genes that are active during development and gamete maturation in black rockfish. Differentially expressed genes (DEGs) were identified and annotated in 4 comparisons (F_III vs. F_IV, F_IV vs. F_V, M_III vs. M_IV and M_IV vs. M_V). Based on analysis of DEGs enriched in the testis, 11 and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were mapped to the M_III vs. M_IV group and the M_IV vs. M_V group, respectively. DEGs in ovarian development were also classified into 10 groups according to their biological functions. The expression patterns of the selected genes determined by qPCR were significantly correlated with the RNA-Seq results, supporting the reliability and accuracy of the RNA-Seq analysis. E2 levels showed down regulation from previtellogenesis to mature stage in female and T level showed down regulation from spermatogenesis to regressed stage in the male.ConclusionsThe categories “intercellular interaction and cytoskeleton”, “molecule amplification” and “repair in the cell cycle” were revealed to be crucial in testis development and spermatogenesis, as was the biosynthesis of a series of metabolites. Our results provide comprehensive insight into black rockfish gonadal development and provide a basis for further study of reproductive physiology and molecular biology in ovoviviparity teleosts.

Boldness Predicts Aggressiveness, Metabolism, and Activity in Black Rockfish Sebastes schlegelii

Animal personality refers to individual behavioral and physiological differences that are consistent over time and across context. Recently, the fish personality has gained increasing attention, especially from the perspective of aquaculture production. Here, we used an important aquaculture species, black rockfishSebastes schlegelii, as the target animal, and conducted a series of experiments to explore the relationships among fish boldness, aggressiveness, locomotor activity, opercular beat rate, standard metabolic rate, and cortisol level. Generally, the results showed that the boldness of black rockfish was significantly, positively correlated with fish aggressiveness, stressed locomotor activity, and standard metabolic rate, while was negatively correlated with stressed opercular beat rate. Bold fish had significantly higher aggressiveness, standard metabolic rate, and stressed locomotor activity but lower stressed opercular beat rate. However, there were no significant correlations between boldness and basal locomotor activity or between boldness and basal cortisol level. These results preliminarily constructed the behavioral and physiological spectrum of black rockfish in the context of fish personality and clearly indicated that the boldness could be used as a discrimination tool to predict fish aggressiveness and metabolic rate, which may have valuable applications for decreasing fish harmful aggression and increasing fish welfare in the aquaculture industry.

Identification of Antimicrobial Peptide Genes in Black Rockfish Sebastes schlegelii and Their Responsive Mechanisms to Edwardsiella tarda Infection.

Simple SummarySebastes schlegelii is a typical viviparous teleost that belongs to the family Scorpaenidae, and is an important mariculture fish in East Asian countries such as Japan, Korea, and China because of its high economic and ecological values. With the enlargement of cultivation scale, bacterial and viral diseases have become the main threats to the farming industry of S. schlegelii, which resulted in significant economic losses. The genome features and evolutionary position of S. schlegelii were investigated based on multiple sequencing approaches. Then, genome-wide identification of AMPs was performed according to the known AMPs in the Antimicrobial Peptides Database. Furthermore, the expression levels of these AMPs were detected to explore their responsive mechanisms to pathogenic bacteria. The availability of the high-quality genome of S. schlegelii will be valuable for understanding its genome features and evolutionary history. Genome-wide AMP identification could be beneficial for understanding the molecular mechanism of innate and adaptive immune responses of S. schlegelii.The black rockfish, Sebastes schlegelii, is a typical viviparous teleost, which belongs to the family Scorpaenidae. Due to its high economic and ecological values, S. schlegelii has been widely cultured in East Asian countries. With the enlargement of cultivation scale, bacterial and viral diseases have become the main threats to the farming industry of S. schlegelii, which have resulted in significant economic losses. In this study, Illumina shotgun sequencing, single-molecule real-time (SMRT) sequencing, 10× genomics and high-throughput chromosome conformation capture (Hi-C) technologies were collectively applied to assemble the genome of S. schlegelii. Then, we identified the antimicrobial peptide genes (AMPs) in the S. schlegelii genome. In total, 214 AMPs were identified in the S. schlegelii genome, which can be divided into 33 classes according to the annotation and cataloging of the Antimicrobial Peptides Database (APD3). Among these AMPs, thrombin-derived C-terminal peptide (TCP) was the dominant type, followed by RegIIIgamma and chemokine. The amino acid sequences of the TCP, cgUbiquitin, RegIIIalpha, RegIIIgamma, chemokine shared 32.55%, 42.63%, 29.87%, 28.09%, and 32.15% similarities among the same type in S. schlegelii. Meanwhile, the expression patterns of these AMPs in nine healthy tissues and at different infection time points in intestine were investigated. The results showed that the numbers and types of AMPs that responded to Edwardsiella tarda infection gradually increased as the infection progressed. In addition, we analyzed the phylogenetic relationships of hepcidins in teleost. The identification of AMPs based on the whole genome could provide a comprehensive database of potential AMPs, and benefit for the understanding of the molecular mechanisms of immune responses to E. tarda infection in S. schlegelii. This would further offer insights into an accurate and effective design and development of AMP for aquaculture therapy in the future.

Altered physiological response and gill histology in black rockfish, Sebastes schlegelii, during progressive hypoxia and reoxygenation.

Hypoxia has gradually become common in aquatic ecosystems and imposes a significant challenge for fish farming. The loss of equilibrium (LOE), 50% lethal time (LT50), plasma cortisol, glucose, red blood cells (RBC), hemoglobin (Hb), gill histological alteration, and related parameters (lamellar length [SLL] and width [SLW], interlamellar distance [ID], basal epithelial thickness [BET], lamellar surface area [LA], and gill surface area [GSA]); respiratory rate; the proportion of the secondary lamellae available for gas exchange (PAGE); and hypoxia-inducible factor (hif-1α, hif-2α) mRNA expression were determined during progressive hypoxia and reoxygenation (R-0, R-12, R-24h) to illustrate the underlying physiological response mechanisms in black rockfish Sebastes schlegelii. Results showed that the DO concentration significantly decreased during progressive hypoxia, while DO at LOE and LT50 were 2.42 ± 0.10mg L-1 and 1.67 ± 0.38mg L-1, respectively. Cortisol and glucose were significantly increased at LOE and LT50, with the highest levels observed at LT50, and then gradually recovered to normal within reoxygenation 24h. RBC number and Hb results were like those of glucose. Hypoxia stress resulted in lamellar clubbing, hypertrophy, and hyperplasia. Respiratory frequency significantly increased at LOE and decreased at LT50. Lamellar perimeters, SLL, ID, LA, GSA, and PAGE, significantly increased at LOE and LT50, with the highest values observed at LT50. However, SLW and BET significantly decreased at LOE, LT50, and R-0. These parameters recovered to nearly normal levels at R-24h. hif-1α mRNAs in gill and liver were significantly upregulated at LOE and LT50, and recovery to normal after reoxygenation 24h. hif-2α mRNAs in gill was similar to that of hif-1α, whereas hepatic hif-2α mRNAs remained unchanged during hypoxia-reoxygenation. These results indicated that progressive hypoxia stress elevated RBC number, Hb, cortisol, and glucose levels, induced the alteration of gill morphology, increased LA and GSA, stimulated respiratory frequency and PAGE, and upregulated the transcription of hif-1α and hif-2α in gill and liver. Reoxygenation treatment for 24h alleviated the stress mentioned above effects. These findings expand current knowledge on hypoxia tolerance in black rockfish Sebastes schlegelii.

Characterization of CYP11A1 and its potential role in sex asynchronous gonadal development of viviparous black rockfish Sebastes schlegelii (Sebastidae)

Mitochondrial cytochrome P450 side-chain cleavage (P450scc), encoded by the cyp11a1 gene, initiates the first step of steroid biosynthesis. In this study, a 1554-bp open reading frame (ORF) of black rockfish (Sebastes schlegelii) cyp11a1 was cloned. The cyp11a1 gene is located on chromosome 5 and has 9 exons. The ORF encodes a putative precursor protein of 517 amino acids, and the predicted cleavable mitochondrial targeting peptide is located at amino acids 1–39. P450scc shares homology with other teleosts and tetrapods, which have relatively conserved binding regions with heme, cholesterol and adrenodoxin. Tissue distribution analysis revealed that the highest expression levels of cyp11a1 were detected in mature gonads and head kidney but that low levels were detected in gestational/regressed ovaries, regressed testes and other tissues. Immunostaining of P450scc was observed in testicular Leydig cells, ovarian theca cells, interrenal glands of head kidney, pituitary and multiple regions of brain. Particularly, two kinds of fish-specific P450scc-positive cells, including coronet cells of brain saccus vasculosus and hypophyseal somatolactin cells, were identified in black rockfish. Our results provide novel evidence for the potential role played by P450scc in reproduction behavior by mediating steroidogenesis in viviparous teleost.

Effect of environmental enrichment on the stress response of juvenile black rockfish Sebastes schlegelii

The stress response is one of the most important aspects of fish welfare in aquaculture. However, relatively few studies focusing on the effect of environmental enrichment on the fish stress response have been conducted, and their limited results were considerably contradictory. The present study aimed to investigate whether the enrichment type and amount had significant effects on the basal stress level and physiological and behavioral responses to acute stress of juvenile black rockfish Sebastes schlegelii. Fish were reared for eight weeks in environments with two enrichment types and three enrichment amounts (i.e., no environmental enrichment control (C), low-amount plant enrichment (PL), medium-amount plant enrichment (PM), high-amount plant enrichment (PH), low-amount structure enrichment (SL), medium-amount structure enrichment (SM), and high-amount structure enrichment (SH)), and subsequently, they were successively subjected to two common acute stressors (i.e., air exposure and confinement) and sampled at 0, 0.5, 1, 3 and 6 h after stress. In general, the plant enrichment groups experienced significantly higher basal stress (indicated by cortisol level and opercular beat rate) than the structure enrichment groups. Meanwhile, no enrichment control group and low-amount enrichment groups experienced significantly higher basal stress than the other two enrichment amount groups. After being subjected to acute stress, the peak cortisol levels of the high-amount enrichment groups were significantly higher than that of the other three enrichment amount groups. The PM, PH and SL fish recovered to basal stress levels at 1 h, the C and PL fish recovered at 3 h, and the SM and SH fish recovered at 6 h after the stress. Moreover, their basal cortisol levels showed strong correlations with peak cortisol levels and recovery time from stress. The correlation between cortisol level and opercular beat rate was also strong. Taken together, these results provide the first evidence to show that enrichment type and amount had significant effects on the fish stress response and might have important applications in fish husbandry and welfare. Based on these results, we suggest that it may be optimal for fish basal stress level and development of an adaptive capacity to provide a medium-amount (approximately 50% floor space coverage) of mixed enrichment in aquaculture.

Effects of environmental enrichment on growth performance, aggressive behavior and stress-induced changes in cortisol release and neurogenesis of black rockfish Sebastes schlegelii

Fish welfare and behavioral flexibility in aquaculture have gained increasing concern among scientists and the public. Stress-related behavioral and physiological responses and neural plasticity are important aspects of fish welfare. Recently, environmental enrichment has been regarded as a promising way to promote fish growth, decrease aggression, and enhance behavioral flexibility; however, relatively few studies focusing on the effects of enrichment and stress on fish neural plasticity have been conducted. In this work, we tested the main and interaction effects of physical enrichment (rearing for eight weeks) and/or acute stress (air exposure and confinement) on the growth performance, aggressive behavior, stress response, and brain expression levels of genes involved in neurogenesis (i.e., proliferating cell nuclear antigen, doublecortin and neuronal differentiation factor; pcna, dcx and neurod, respectively) of juvenile black rockfish Sebastes schlegelii. In general, environmental enrichment treatment significantly decreased fish aggressive behavior and the levels of basal cortisol, while it enhanced the gene expression levels of pcna and dcx in the brain. As expected, the fish exposed to acute stress had significantly higher levels of cortisol and brain pcna gene expression compared with fish at a basal status. Enrichment and stress had significant interaction effect on fish cortisol levels. Furthermore, statistically significant correlations (P < .05) between aggressive behavior and stress response (indicated by cortisol level) and between cortisol and neurogenesis biomarkers (especially pcna) were observed. The growth performance of the enriched fish was statistically similar to that of the barren-reared fish. No main or interaction effect of enrichment and stress on brain neurod gene expression was detected. This is the first evidence showing that environmental enrichment and acute stress can produce significant effects on processes of fish neurogenesis. These findings confirm the positive effects of environmental enrichment on fish stress responses and neurogenesis in the context of acute stress, which may lay the foundation for improved welfare and behavioral flexibility of fish in the aquaculture industry.

Genetic Assessment of a Black Rockfish, Sebastes schlegelii, Stock Enhancement Program in Lidao Bay, China Based on Mitochondrial and Nuclear DNA Analysis

The black rockfish Sebastes schlegelii is a commercially important fish species for marine fishery stock enhancement in Asia. This work aimed to evaluate the potential genetic impacts of releasing hatchery-reared juvenile black rockfish on wild stock in Lidao Bay, China. A partial sequence of the mitochondrial DNA (mtDNA) control region and 38 microsatellite DNA loci were used to assess the genetic impact. The haplotype diversity parameter (h) and nucleotide diversity parameter (π) in hatchery-released stock were 0.902 and 0.00483, respectively. The h values in wild stock before stock enhancement and the mixed stock after enhancement were 0.970 and 0.939, respectively, and the π values were 0.00581 and 0.00526, respectively. The mean effective numbers of alleles (Ne) in hatchery-released stock was 4.76, the mean polymorphism information content (PIC) was 0.674, the observed heterozygosity (Ho) was 0.668, and the expected heterozygosity (He) was 0.697. In wild stocks before stock enhancement and the mixed stock after enhancement, the Ne, PIC, Ho, and He values were 6.01 and 5.82, 0.698 and 0.716, 0.709 and 0.741, and 0.735 and 0.754, respectively. These results showed that there was no marked decrease in the hatchery-released stock, although it displayed slightly lower levels of genetic diversity and heterozygosity than the wild stock. The mixed stocks after S. schlegelii release exhibited similar genetic diversity to that of the wild stock before release, and the genetic variation in the natural stock did not decrease after stock enhancement. Moreover, both the fixation index (FST) and AMOVA analysis clearly showed minimal population structure differences between the hatchery-released and wild stocks, and the wild stock before enhancement and the mixed stock after enhancement. These results showed that stock enhancement may not cause any negative genetic effects on wild S. schlegelii stock in Lidao Bay over the short term. Accordingly, we propose that the current breeding and release methods are appropriate for conserving the genetic diversity of S. schlegelii. However, our results also showed a slight reduction in some genetic parameters, such as allelic diversity, heterozygosity, and effective population size, in the mixed stock after restoration. Consequently, long-term genetic evaluation might be required.

Effects of environmental enrichment on the welfare of juvenile black rockfish Sebastes schlegelii: Growth, behavior and physiology

Environmental enrichment is a promising way to enhance fish welfare in aquaculture. However, the observed effects of enrichment on fish growth, behavior and physiology vary widely among studies, and few studies have focused on the quantification of enrichment. The present study aimed to investigate whether enrichment type and level significantly affect the growth performance, aggressive behavior, cortisol level and brain monoaminergic activities of juveniles of the black rockfish Sebastes schlegelii. Juveniles were reared for eight weeks under different combinations of enrichment type and enrichment level: no environmental enrichment (C), low-level plant enrichment (PL), medium-level plant enrichment (PM), high-level plant enrichment (PH), low-level structure enrichment (SL), medium-level structure enrichment (SM) and high-level structure enrichment (SH). Subsequently, behavioral and physiological parameters were determined. In general, the growth performance, feed intake and food conversion efficiency of C, PM, PH and SL fish were relatively higher than those of fish from the other treatments. Low-level plant treatment produced the highest levels of aggressive behavior, cortisol and brain serotonergic system activity, whereas the medium- and high-level structure treatments yielded the lowest levels of these stress-related behavioral and physiological indicators. C fish had significantly higher stress levels than PM, PH and SL fish. No significant difference among treatments was observed in the condition factor, coefficient of weight variation, locomotor activity, growth hormone level or brain dopaminergic system activity. Taken together, these results provide the first evidence to show that the type and level of environmental enrichment have interaction effects on fish growth performance, behavioral phenotype (especially aggressive behavior) and stress-related physiological processes. Since the control fish had significantly higher stress levels than the fish exposed to medium- and high-level plant enrichment and low-level structure enrichment, we suggest that enriching approximately 50% basal area coverage with objects might be optimal for enhancing fish welfare. Moreover, a possible conceptual model is presented to interpret the effects of enrichment on fish welfare.

Characterization, expression, enzymatic activity, and functional identification of cathepsin S from black rockfish Sebastes schlegelii

Cathepsin S belong to the cathepsin L-like family of cysteine cathepsins. It is well known that Cathepsin S participate in various physiological processes and host immune defense in mammals. However, in teleost fish, the function of cathepsin S is less investigated. In the present study, a cathepsin S homologue (SsCTSS) from the teleost fish black rockfish (Sebastes schlegelii) were identified and examined at expression and functional levels. In silico analysis showed that three domains, including signal peptide, cathepsin propeptide inhibitor I29 domain, and functional domain Pept_C1, were existed in the cathepsin. SsCTSS possesses a peptidase domain with three catalytically essential residues (Cys25, His162, and Asn183). Phylogenetic profiling indicated that SsCTSS are evolutionally close to the cathepsin S of other teleost fish. The expression of SsCTSS in immune-related tissues was upregulated in a time-dependent manner upon bacterial pathogen infection. Purified recombinant SsCTSS (rSsCTSS) exhibited apparent peptidase activity, which was remarkably declined in the presence of the cathepsin inhibitor E−64. rSsCTSS showed strong binding ability to LPS and PGN, the major constituents of the outer membranes of Gram-negative and Gram-positive bacteria, respectively. rSsCTSS also exhibited the capability of agglutination to different bacteria. The knockdown of SsCTSS attenuated the ability of host to eliminate pathogenic bacteria. Taken together, our results suggested that SsCTSS functions as cysteine protease which might be involved in the antibacterial immunity of black rockfish.

Effects of different levels of environmental enrichment on the sheltering behaviors, brain development and cortisol levels of black rockfish Sebastes schlegelii

Environmental enrichment is a promising way to increase the fitness and survival of fish released for stock enhancement and biological conservation programs. However, the effects of enrichment in different studies on the fish behavior, physiology and neural development were considerably different. The present study aimed to investigate whether enrichment levels had significant effects on the shelter-seeking behavior, risk-taking behavior, brain compartments size, growth performance, stress level and immune function of black rockfish Sebastes schlegelii. Larval fish were reared for four (post-larval fish) and seven (juvenile fish) weeks in environments with three enrichment levels (i.e., no environmental enrichment items (C), few environmental enrichment items (EF) and many environmental enrichment items (EM)); subsequently, the behavioral and physiological parameters were determined. In general, juvenile fish reared with few enrichment items had significantly better specific growth rate and final body weight, but higher whole-body cortisol levels than EM and C fish. Meanwhile, the muscle acid phosphatase (ACP), alkaline phosphatase (AKP) and total superoxide dismutase (T-SOD) activities of EM juveniles were better than those of either C or EF fish generally. Enrichment did not affect the two types of sheltering behaviors or the relative cerebellum volumes during the post-larval stage, while the conditions changed during the juvenile stage. The proportion to seek shelter successfully of EF juveniles was significantly higher compared to that of other treatments, and few enrichment items also reduced maladaptive risk-taking behavior, i.e., EF juveniles took a longer time to leave the shelters. The relative cerebellum area of EF juveniles was significantly larger than that of either C or EM fish, while no significant differences were detected in other sub-brain areas. These results indicate that enrichment levels indeed had significant effects on the fish behavioral phenotype, brain plasticity and physiological condition, and in our experimental design, the fish reared with few enrichment items showed more natural sheltering behaviors and brain phenotypes and EF treatment could be beneficial for the fitness of released fish, however, more adaptive behaviors (e.g., foraging behavior, competitive ability) and field survival rate need to be investigated to validate our conclusions.

Molecular Characterization and Expression Analysis of Interferon Regulatory Factor 8 (IRF8) in the Black Rockfish Sebastes schlegelii

Molecular Characterization and Expression Analysis of Interferon Regulatory Factor 8 (IRF8) in the Black Rockfish Sebastes schlegelii

Short-Term Fidelity, Habitat Use and Vertical Movement Behavior of the Black Rockfish Sebastes schlegelii as Determined by Acoustic Telemetry.

The recent miniaturization of acoustic tracking devices has allowed fishery managers and scientists to collect spatial and temporal data for sustainable fishery management. The spatial and temporal dimensions of fish behavior (movement and/or vertical migrations) are particularly relevant for rockfishes (Sebastes spp.) because most rockfish species are long-lived and have high site fidelity, increasing their vulnerability to overexploitation. In this study, we describe the short-term (with a tracking period of up to 46 d) spatial behavior, as determined by acoustic tracking, of the black rockfish Sebastes schlegelii, a species subject to overexploitation in the Yellow Sea of China. The average residence index (the ratio of detected days to the total period from release to the last detection) in the study area was 0.92 ± 0.13, and most of the tagged fish were detected by only one region of the acoustic receiver array, suggesting relatively high site fidelity to the study area. Acoustic tracking also suggested that this species is more frequently detected during the day than at night in our study area. However, the diel detection periodicity (24 h) was only evident for certain periods of the tracking time, as revealed by a continuous wavelet transform. The habitat selection index of tagged S. schlegelii suggested that S. schlegelii preferred natural reefs, mixed sand/artificial reef bottoms and mixed bottoms of boulder, cobble, gravel and artificial reefs. The preference of this species for the artificial reefs that were recently deployed in the study area suggests that artificial seascapes may be effective management tools to attract individuals. The vertical movement of tagged S. schlegelii was mostly characterized by bottom dwelling behavior, and there was high individual variability in the vertical migration pattern. Our results have important implications for S. schlegelii catchability, the implementation of marine protected areas, and the identification of key species habitats, and our study provides novel information for future studies on the sustainability of this important marine resource in eastern China.