Several exogenous probiotics are applicable in fish culture; however, challenges in isolation and verification have hindered the full utilization of numerous host probiotics. Therefore, this study aimed to apply the host probiotic Exiguobacterium acetylicum G1-33 to hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) cultures and explore its mechanism of action. In total, 360 hybrid grouper were divided into four groups, which were fed the following for 60 days: three received commercial feed with varying concentrations of E. acetylicum G1-33 (10⁶, 10⁸, and 10¹⁰ CFU/g), while a control group received commercial feed. The results showed that supplementation with 10⁶ and 10⁸ CFU/g of E. acetylicum G1-33 enhanced gut morphology, upregulated growth-related genes (ghr1, igf-2, s6k1, tor), and promoted growth, with supplementation with 10⁸ CFU/g resulting in the most notable enhancement. However, supplementation with 10¹⁰ CFU/g inhibited growth, possibly because of changes in intestinal morphology. Additionally, supplementation with E. acetylicum G1-33 upregulated the expression of immune-related genes (c3, myd88, Cu/Zn-sod, tlr3, and tnf2) in the liver and head kidney but led to an increase in malondialdehyde content, as well as a decrease in alkaline phosphatase and acid phosphatase activities, in the liver and serum, indicating increased oxidative stress. Moreover, supplementation with 10⁶ and 10⁸ CFU/g E. acetylicum G1-33 enhanced the widespread expression of immune-related genes in the head kidney and liver, respectively, and improved resistance to Vibrio harveyi, whereas supplementation with 10¹⁰ CFU/g weakened this resistance. In conclusion, E. acetylicum G1-33, particularly at 10⁸ CFU/g, emerged as an effective probiotic, optimizing growth performance and immunity in hybrid grouper. This research is pioneering in its application of E. acetylicum in mariculture, potentially broadening the range of probiotic strategies in aquaculture.

The greater amberjack (Seriola dumerili) is an emerging marine fish that is increasingly favored in aquaculture. Currently, there are few studies on the development and regulation of greater amberjack ovaries. In this study, the ovary transcriptome profiles of greater amberjack at three different stages (stage II, III, and IV) were performed, and identified the genes and pathways that may play significant roles in the processes of follicle growth and maturation. A total of 6597, and 1061 differentially expressed genes (DEGs) were detected in FII vs. FIII, FIII vs. FIV, and FII vs. FIV stages, respectively. GO and KEGG enrichment analyses revealed that these DEG_S are primarily involved in steroid hormone biosynthesis (e.g., cyp11a1, cyp17a1, cyp19a1a, hsd3b1, esr1), lipid metabolism (e.g., plpp3, lpl, pld1, and fabp10a), and meiotic arrest and resumption (e.g., pgr, arb, ccnd2, adcy2, adcy9, myl9, calm1). Additionally, several signaling pathways involved in ovarian development have been identified, including the PI3K-Akt, Wnt, TGF-beta, GnRH, and immune-related signaling pathways. qPCR results of nine representative genes related to steroid hormone synthesis and cell growth verified the reliability of the generated RNA-seq data. This research contributes to our comprehension of the molecular processes underlying ovarian growth and maturation in marine fishes and provides a theoretical basis for the investigation of functional genes associated with oogenesis in greater amberjack.

Environmental temperature declines significantly impact the physiological processes of marine organisms, particularly under the cool La Nina conditions, challenging yellowfin tuna (Thunnus albacares) aquaculture. Low temperatures affect fish metabolism and immune functions and can alter the gut microbiota composition, influencing health and growth. This study investigates the impact of low temperatures on the gut microbiota of juvenile yellowfin tuna. Fish were divided into a Low Temperature (LT) group (24 °C), an Ultra Low Temperature (ULT) group (18 °C), and a Control group (CG) (30 °C), with evaluations at 0, 12, 24, and 36 h using α-diversity analysis and microbial species composition. Results indicated a significant increase in the Ace index for the ULT group after 36 h of cold stress (p < 0.05), with no significant changes in the Shannon index. A decline in Proteobacteria and increases in Verrucomicrobiota and Firmicutes were observed in both LT and ULT groups. Additionally, both LT and ULT groups showed a significant rise in the Ace index at 36 h (p < 0.05), with a significant decrease in the Shannon index in the ULT group at 24 h. Furthermore, Firmicutes significantly increased at 12 h in both temperature groups (p < 0.05). These findings highlight the potential role of the gut microbiome in adapting yellowfin tuna to cold environments and provide microbial insights into their physiological adaptations, laying a foundation for further research and practical applications in aquaculture under cold conditions.

The greater amberjack (Seriola dumerili) is a globally important aquaculture fish species belonging to the family Carangidae. However, current research on the ovarian development and regulation of the greater amberjack is limited, particularly with regard to early ovarian development in artificially bred individuals. Therefore, this study aims to analyze the ovarian transcriptomes at the primary growth stage in one-year-old fish at the chromatin nucleolar stage and two-year-old fish at the perinucleolar stage to suggest how early ovarian development takes place in artificially bred greater amberjacks. To do this, the study constructed ovarian mRNA expression profiles of different stages of artificially bred fish and identified differentially expressed genes (DEGs), Gene Ontology terms, and Kyoto Encyclopedia of Genes and Genomes pathways important for various physiological processes. A functional analysis revealed that the DEGs closely related to ovarian development were involved in cell growth and death (e.g., ccnd1, cdk1, cdc6, cdc25b, fbxo43, cdkn1a and cdkn1d), the TGF-beta signaling pathway (e.g., gdf6, bmpr1b, gsdf, amh, tgfb3, and smad6), steroid hormone biosynthesis (e.g., hsd3b1, hsd11b2, hsd17b12 and hsd20b2), and the endocrine system (e.g., mapk8a, mapk11, mapk12a, mapk13 and adcy9). These findings suggest that ovarian development is the result of the coordinated regulation of various genes responsible for various functions. This study provides a theoretical basis for exploring the underlying molecular mechanisms of early ovarian development in artificially bred greater amberjacks.

Humphead wrasse, Cheilinus undulatus, is an endangered fish species with high economic and ecological value as well as natural sex change from female to male, while sexual selection occurs in breeding aggregations. In our present study, we constructed the first gap-free telomere-to-telomere (T2T) genome assembly for humphead wrasse, by integration of PacBio HiFi, ONT Ultra-long and Hi-C sequencing techniques. With 99% of the entire sequences anchored into 24 chromosomes, this haplotypic genome assembly spans approximately 1.25 Gb and presents a complete set of 48 telomeres and 24 centromeres. In terms of correctness (quality value QV: 53.447) and completeness (BUSCO score: 99.3%), this chromosome-scale assembly is indeed of high quality. We predicted 658.03 Mb of repetitive sequences and annotated 26,609 protein-coding genes in the assembled genome. This high-quality T2T genome assembly not only facilitates the genetic conservation of humphead wrasse, but also offers fundamental genomic data for supporting in-depth investigations on functional genomics, genetic diversity, and selective breeding for this economically important teleost.

Epinephelus akaara is one of the aquaculture species with high commercial value in the aquaculture industry in the Asia-Pacific region. However, acute hypoxia is widespread in the intensive farming and live fish transportation of E. akaara, which seriously hinders the rapid development of the E. akaara farming industry. In this study, transcriptome sequencing (RNA-seq) was conducted on the liver tissues of E. akaara after hypoxia (0.6 ± 0.1 mg/L) for 1, 3, 6 and 9 h. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that key signaling pathways such as IL-17, HIF-1, TNF and PI3K/Akt were significantly enriched in the hypoxia treatment groups (Hy6 and Hy9). Reverse transcription quantitative polymerase chain reaction (RT-qPCR) analyses revealed that genes linked to energy metabolism, immune response and apoptosis changed significantly in the liver and brain at 6 h and 9 h under acute hypoxia. In addition, three metabolism-related enzymes (GLU, LDH and PK) and two immune-related enzymes (ALT and AKP) all changed significantly at 6 h and 9 h, indicating that 6–9 h was the critical period for physiological stress of E. akaara. In conclusion, these results indicate that E. akaara mediated the organism’s tolerance and adaptation to hypoxic stress by regulating energy metabolism, immune response and apoptosis. This study enriches the regulatory mechanism by which E. akaara adapts to acute hypoxia and is conducive to the breeding of hypoxia-tolerant E. akaara strains.