Search Results (9)

Korean rockfish, Sebastes schlegeli, a coastal species, is vulnerable to pollutants such as microplastics and bacteria. While interactions between microplastics and other pollutants have been studied, little is known about microplastic and bacteria interactions. This study examined the effects of combined exposure to polystyrene microplastics in the form of microbeads (MB; 0.2 µm, 5 and 50 beads/L) and Streptococcus iniae (1 × 10⁵ and 1 × 10⁷ CFU/mL) for five days on oxidative stress and apoptosis in Korean rockfish. We assessed the mRNA expression and activity of oxidative stress markers (SOD, CAT, H₂O₂, NO, CYP1A1, GST), plasma LPO levels, and caspase-3 expression in liver tissue. Co-exposure to high MB and S. iniae concentrations significantly elevated oxidative stress and apoptosis markers, suggesting enhanced toxicity. This may result from MB facilitating pathogen transport into the fish, indicating microplastics can act as vectors for bacterial infection in aquatic environments. Full article

The current experiment is conducted to determine the effects of chicken by-product meal (CBM) as a fish meal (FM) replacer in diets, with or without the inclusion of jack mackerel (Trachurus japonicus) meal (JMM), on the growth and feed availability of rockfish (Sebastes schlegeli). A two-way ANOVA experimental design [FM replacement level (FMRL, 25% and 50%) × JMM inclusion (without and with)] was adopted. The control (Con) diet contained 55% FM. In the Con diet, 25% and 50% of FM were substituted with CBM, either without or with the inclusion of 22% JMM, referred to as the CBM25, CBM50, CBM25J, and CBM50J diets, respectively. A total of 375 juvenile fish were distributed into 15 tanks with triplicates. The 25% FM replacement diets led to significantly (p < 0.003 and p < 0.004, respectively) greater weight gain and specific growth rate (SGR) of rockfish than the 50% FM replacement diets. Furthermore, the CBM-replaced diets with JMM inclusion led to significantly (p < 0.003 and p < 0.002, respectively) greater weight gain and SGR of fish compared with those without JMM inclusion. Weight gain and SGR of rockfish fed the Con and CBM25J diets were significantly (p < 0.001 for both) greater than those of fish fed the CBM25, CBM50, and CBM50J diets. However, neither dietary FMRL nor JMM inclusion had significant (p > 0.05) effects on feed consumption, blood chemistry, or the biochemical composition of rockfish. In conclusion, 25% of FM could be replaced with CBM in the 55% FM-based diet, including JMM, without adverse effects on the growth, feed availability, blood chemistry, or biochemical composition (proximate composition and amino and fatty acid profiles) of rockfish. Full article

A 56-day feeding experiment was carried out to evaluate the effects of substituting fish meal (FM) with chicken by-product meal (CBM) in diets on the growth and feed utilization of rockfish (Sebastes schlegeli). Six experimental diets were formulated to be isonitrogenous and isolipidic. The control (Con) diet included 55% FM. In the Con diet, 10%, 20%, 30%, 40%, and 50% of FM was replaced with CBM, named as the CBM₁₀, CBM₂₀, CBM₃₀, CBM₄₀, and CBM₅₀ diets, respectively. A total of 540 juvenile fish were distributed into 18 tanks (30 fish per tank and 3 tanks per diet) and fed to apparent satiation two times daily for 56 days. The weight gain and specific growth rate of rockfish fed the CBM₁₀ and CBM₂₀ diets were comparable to rockfish fed the Con diet. The feed consumption of rockfish fed the Con and CBM₁₀ diets was significantly (p < 0.001) higher than that of fish fed all other diets, except for the CBM₂₀ diet. However, protein retention, biometric indices, chemical composition, amino acid profiles, and plasma and serum parameters of rockfish were not significantly influenced by dietary FM substitution with CBM. The Con, CBM₁₀, and CBM₂₀ diets showed superior (p < 0.001) economic profit index (EPI) compared to the CBM₃₀, CBM₄₀, and CBM₅₀ diets. Conclusively, FM up to 20% could be substituted by CBM in diets without impairing growth, feed availability, chemical composition, amino acid profiles, and blood parameters of rockfish grown from 2.5 g to 12.5 g. However, the long-term effects of CBM substitution or the potential use of combined CBM and other alternative protein sources for FM in rockfish diets are needed in future. Full article

A two-way {dietary substitution source [chicken by-product meal (CBM), meat meal (MM), and tuna by-product meal (TBM)] × substitution level (25% and 50%)} ANOVA experimental design was adopted. The control (Con) diet included 55% FM. In the Con diet, 25% and 50% of FM were substituted with CBM, MM, and TBM, with the inclusion of 22% JMM exhibiting strong attractiveness for rockfish, named CBM25J, CBM50J, MM25J, MM50J, TBM25J, and TBM50J diets, respectively. All experimental diets were assigned to triplicate groups of fish. A total of 525 juvenile fish were distributed into 21 flow-through tanks. The CBM- and TBM-substituted diets achieved greater weight gain and specific growth rates (SGRs) of rockfish than the MM-substituted diets. Moreover, dietary 25% FM substitutions achieved greater weight gain and SGRs of rockfish than dietary 50% FM substitutions. Weight gain and SGRs of rockfish fed the Con, CBM25J, and TBM25J diets were superior to those of rockfish fed the CBM50J, MM50J, and TBM50J diets. Dietary 25% FM substitutions exhibited higher rockfish feed consumption than dietary 50% FM substitutions. None of the proximate compositions, amino and fatty acid profiles, or blood chemistry of the fish were significantly different among dietary treatments. The highest EPI was observed in the CBM25J diet. Conclusively, a 25% FM substitution with CBM, MM, and TBM with the inclusion of 22% JMM in the 55% FM-based diet could be made without reducing the growth and feed consumption of rockfish. Finally, the CBM25J diet produced the highest weight gain and SGRs of rockfish, as well as the highest economic return to farmers. Full article

Background: Hypoxia triggers stress, leading to significant alterations in gene expression patterns, which in turn affect fish’s growth and development. Real-time quantitative PCR (RT-qPCR) is a pivotal technique for assessing changes in gene expression. However, its accuracy is highly contingent upon the stable expression of reference genes. Ribosomal RNA (18s), β-actin (actb), elongation factor 1-α (ef1a), α tubulin (tuba), and ribosomal protein L17 (rpl17) are the widely used reference genes, but their expression stability in the tissues of black rockfish under hypoxic conditions remains unclear. Methods: The expression of genes was detected by RT-qPCR and the stability was assessed by Delta Ct, geNorm, NormFinder, and BestKeeper algorithms. Results: Results showed that tuba exhibited stable expression in liver, heart, gill tissues under normoxic conditions, and in the liver and head kidney under hypoxic conditions. Ef1a was identified as the most stably expressed gene in gill tissue under hypoxia. For hypoxic heart studies, rpl17 and tuba were recommended as reference genes. 18s showed high stability in spleen tissue under hypoxic conditions. Actb was the most stably expressed gene in spleen and head kidney tissues under normoxic conditions. Conclusions: The identified reference genes exhibited tissue-specific stability, and it was necessary to select appropriate reference genes based on the specific tissue type for gene expression studies under hypoxic conditions. These findings help in enhancing the accuracy of gene expression analysis in the mechanism of hypoxia for black rockfish. Full article

The rockfish (Sebastes schlegeli) and striped beakperch (Oplegnathus fasciatus) were released in marine ranching areas in Korea, Japan, and China to maintain fishery resources in coastal areas. To estimate the density and biomass of fishery resources, the target strength (TS) of target marine organisms is needed to scale integrated volume backscattering coefficients. In this study, the target strength–length (TS–L) relationship for live rockfish and striped beakperch was derived using ex situ methods at a frequency of 200 kHz. The TS-L function for rockfish and striped beakperch can be expressed as TS_Avg. = 20logTL − 69.25 (R² = 0.35) and TS_Avg. = 20logFL − 67.01 (R² = 0.31), respectively. These results can be used to assess the growth, density, and abundance of the two species using acoustics. Full article

This study was conducted to elucidate the impact on the growth and feed availability of rockfish (Sebastes schlegeli) from including jack mackerel meal (JMM) in feeds which otherwise substitute 20% fish meal (FM) with chicken by-product meal (CBM). Six formulated feeds were designed to be isonitrogenous and isolipidic. Specifically, 55% FM was included in the control (Con) diet. In the Con diet, 20% FM was substituted by CBM, and then the graded levels (0, 20, 40, 60, and 80%) of JMM were included instead of FM, named as the C20J0, C20J20, C20J40, C20J60, and C20J80 diets, respectively. Five hundred and forty juvenile rockfish (initial weight of 11.2 g) were assigned to 18 tanks. All experimental feeds were fed to triplicate groups of rockfish twice daily for 8 weeks. Superior weight gain, specific growth rate (SGR), and feed intake of rockfish fed the C20J60 and C20J80 diets compared to rockfish fed the Con and C20J0 diets were observed. However, the feed utilization, biological indices, proximate composition, amino acid profiles, and blood chemistry of the rockfish were not affected by the dietary treatments. The slightly but not significantly higher economic profit index and growth performance were obtained in the C20J60 diet compared to the C20J80 diet. In conclusion, the C20J60 diet was the most recommendable treatment based on the improvement in growth performance (weight gain and SGR) and feed intake of rockfish, and the highest economic return to farmers. Full article

This experiment was performed to assess the substitution impact of fish meal (FM) with tuna by-product meal (TBM) in feeds on growth and feed availability of the early stage of juvenile rockfish (S. schlegeli). Six experimental feeds were prepared to be isonitrogenous and isolipidic. Fifty-five percent of FM was contained in the control (Con) diet. In the Con diet, 20, 40, 60, 80, and 100% FM were replaced by TBM, named the TBM₂₀, TBM₄₀, TBM₆₀, TBM₈₀, and TBM₁₀₀ diets, respectively. A total of 540 early-stage juvenile rockfish averaging 2.4 g was divided into 18 tanks and hand-fed to satiation for 56 days. Weight gain and feed consumption of rockfish fed the TBM₂₀ and TBM₄₀ diets were comparable to rockfish fed the Con diet. The specific growth rate (SGR) of rockfish fed the Con diet was comparable to rockfish fed the TBM₂₀, TBM₄₀, and TBM₆₀ diets. Feed efficiency, biometric indices, hematological parameters, proximate composition, and amino acid profiles of rockfish were not impacted by dietary treatments. The economic profit index (EPI) of the Con, TBM₂₀, and TBM₄₀ diets were higher than that of all other diets. FM up to 40% could be substitutable with TBM in the diets of rockfish without deteriorating weight gain and feed consumption, but producing the highest EPI. Full article

Four pathogenic Vibrio species were isolated from three diseased black rockfish Sebastes schlegeli in Yantai, Shandong Province, China. The strains were identified based on physiological and biochemical characteristics and 16S rDNA sequencing and named SF-2, SF-3, SF-5, and SF-6, respectively. SF-2 was Vibrio scophthalmi, SF-3 was V. harveyi, SF-5 was V. alginolyticus, and SF-6 was V. parahaemolyticus. This is the first time that V. scophthalmi was isolated from black rockfish. The present research shows that V. scophthalmi is a potential pathogen. Detection of virulence genes using polymerase chain reaction showed that SF-3, SF-5, and SF-6 carried FlaB; SF-5 and SF-6 carried TcpA; and SF-2, SF-5, and SF-6 carried ToxS. Tdh, Trh, Tlh, ToxR, and Zot were not detected. SF-3, SF-5, and SF-6 all had protease, gelatinase, lipase, and lecithinase. They were all intermediately sensitive to erythromycin, whereas SF-2, SF-5, and SF-6 were sensitive to spectinomycin, and SF-3 was sensitive to cotrimoxazole and chloramphenicol. They were resistant to most antibiotics and multidrug resistance was obvious. Full article