Search Results (57)

Background: Aquaculture increasingly seeks sustainable alternatives to fishmeal, a key protein source in fish diets. Black Soldier Fly Larvae (BSFL) meal is a promising substitute, but its effects on fish growth, immunity, and gut health need further investigation. This study aimed to evaluate the impact of varying BSFL inclusion levels on juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂), a widely farmed species in tropical aquaculture. Methods: Juvenile hybrid grouper were fed diets with four levels of BSFL substitution (0%, 10%, 30%, and 50%) over 56 days. Key metrics such as growth performance, immune function, antioxidant capacity, and gut transcriptome were analyzed. Results: Replacing fish meal with BSFL meal had no significant effect on the survival rate of hybrid grouper (p > 0.05) but significantly affected growth performance, immune function, and antioxidant capacity (p < 0.05). BSFL10 and BSFL30 groups showed good growth and elevated immune enzyme activity, with significantly higher HIS levels (p < 0.05); the Wf of the BSFL10 group was comparable to the control. However, excessive replacement (BSFL50) led to reduced growth (Wf significantly lower, p < 0.05) and increased oxidative stress, as indicated by higher CAT activity (p < 0.05). Transcriptomic analysis revealed upregulation of immune- and metabolism-related genes with increasing BSFL levels, with immune pathways notably activated in the BSFL50 group. Conclusions: BSFL meal is a promising alternative to fishmeal in juvenile hybrid grouper diets, with moderate inclusion (10–30%) being most beneficial. Excessive BSFL substitution (50%) may impair fish health, highlighting the need for careful formulation in aquaculture diets. Full article

Groupers are important aquaculture species, and hybridization is an effective breeding method for genetic improvement and to enhance production efficiency in groupers. The ShanHu grouper (Epinephelus fuscoguttatus ♀ × Epinephelus polyphekadion ♂) is a hybrid grouper with potential for aquaculture development and research value. Using Illumina and PacBio sequencing platforms, as well as PacBio SMRT technology and Hi-C auxiliary mounting technology, the whole genome sequencing and assembly of the ShanHu grouper were completed, resulting in a chromosome-level genome information for this hybrid grouper. The genome assembly has a total length of 1.17 Gb with a scaffold N50 of 46.12 Mb, and 171 contigs were anchored into 24 chromosomes. Additionally, its repeat sequences and non-coding RNAs were annotated and 26,102 genes were predicted. Through comparative genomic analysis of the hybrid species ShanHu grouper and its parents, we found that comparative genomic analyses revealed centric inversion structural variations on the chromosomes of the hybrid ShanHu grouper in relation to the brown-marbled grouper and the camouflage grouper. Furthermore, the gene families of the hybrid species have expanded in pathways related to immunity and growth development. This study is the first to provide complete genomic information for a hybrid grouper, offering its full genetic information, exploring the genetic variations in the genomes of hybrid offspring, and providing data references for foundational theoretical research and grouper production practices. Full article

Evaluating the interaction between dissolved oxygen (DO) and feeding rates (FRs) in fish is crucial for the precise regulation of aquaculture water environments. This study established four treatment groups: the CK group (DO = 6 mg/L, FR = 2% of body weight), the HFR group (DO = 6 mg/L, FR = 3.5% of body weight), the HDO group (DO = 9 mg/L, FR = 2% of body weight), and the MIX group (DO = 6 mg/L, FR = 3.5% of body weight). The combined effects of dissolved oxygen and feeding levels on oxidative stress, biochemical indicators, and growth in the hybrid grouper were evaluated. The results showed that mild hyperoxia significantly upregulates the expression of antioxidant enzyme genes (cat, cu/zn-sod, and gpx1a). Under conditions of mild hyperoxia, an increased feed rate can significantly downregulate the expression of cat and gpx1a. Additionally, serum levels of carnosine and cndp1 in muscle tissue are significantly elevated. Furthermore, a high FR mitigates the downregulation of glucose, triglycerides, and alanine aminotransferase (ALT) induced by mild hyperoxia while alleviating the upregulation of aspartate aminotransferase (AST). The combined effects of mild hyperoxia and high FR significantly enhance final body weight and specific growth rate (SGR), with notable interactions observed. Mild hyperoxia reduces serum levels of bile acids and glycocholic acid under high feeding conditions while significantly downregulating the expression of ghrb in both liver and brain tissues. In summary, high FRs alleviate oxidative stress and energy substrate deficiency in juvenile hybrid grouper under mild-hyperoxia environments. Moreover, the synergistic effect between mild hyperoxia and high FR promotes growth by improving bile acid enterohepatic circulation. This study provides a reference for the regulation of DO and feeding in modern industrial intensive mariculture. Full article

This experiment was to investigate the effects of feeding frequency on the growth performance, body composition, and intestinal health of hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatu ♂). Fifty-six days of feeding with four different feeding frequencies (1 time/day, 2 times/day, 3 times/day, and 4 times/day) were conducted on groupers with an initial body weight of 11.51 ± 0.02 g. The results show the following: (1) Weight gain rate (WGR) and specific growth rate (SGR) of the groupers in the 1 time/day group were significantly lower than in other groups (p < 0.05). (2) Superoxide dismutase (SOD) had the lowest value in the 1 time/day group, significantly lower than the 2 times/day and 4 times/day groups, catalase showed an upward trend, and the 4 times/day group was significantly greater than the other groups (p < 0.05). The total antioxidant capacity (T-AOC) and glutathione peroxidase (GPX) activities in the 1 time/day group were significantly lower than in the other groups (p < 0.05). (3) The increase in feeding frequency led to a significant increase in the expression levels of cat and il-6 (p < 0.05). In summary, appropriate feeding frequency can promote growth and enhance the antioxidant capacity of the fish’s gut. We recommend a best feeding frequency of 2 times/day. Full article

A 10-week feeding study was conducted to examine the effects of dietary tryptophan (Trp) levels on the growth performance and protein metabolism of hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) with the aim of determining the optimal Trp requirement. Six isonitrogenous and isolipidic experimental diets were formulated, containing varying levels of Trp (0.26%, 0.32%, 0.42%, 0.46%, 0.58%, and 0.62% of diet). Each diet was administered to 90 hybrid groupers with an initial average weight of 10.52 ± 0.02 g. Dietary levels of 0.32–0.62% Trp generally promoted growth performance and feed utilization in hybrid grouper, with the 0.46% Trp level demonstrating the highest weight gain and protein efficiency ratio. Furthermore, fish fed with 0.46% Trp exhibited higher activities of intestinal lipase and amylase compared to other groups. Furthermore, the activities of Trp metabolism-related enzymes in the liver were markedly elevated by this Trp level, including indoleamine 2,3-dioxygenase, 5-hydroxytryptophan decarboxylase, and tryptophan-2,3-dioxygenase. Additionally, a dietary level of 0.46% Trp resulted in a substantial increase in the activities of protein metabolism-related enzymes such as adenosine monophosphate deaminase and glutamate dehydrogenase in the liver. Dietary levels of 0.32–0.46% Trp activated the hepatic mammalian target of rapamycin pathway, while a dietary 0.46% Trp level inhibited the hepatic amino acid response signaling pathway. In summary, suitable dietary Trp levels enhanced intestinal digestive enzyme activities, facilitated both protein synthesis and catabolism, and ultimately improved growth performance in hybrid grouper. Analysis using a second-order regression curve of weight gain and protein efficiency ratio indicated that the optimal dietary Trp requirement for hybrid grouper ranged from 0.41–0.46% of diet (0.82–0.92% of dietary protein). Full article

Triploid fish sometimes grow faster and larger than diploids, making them valuable in aquaculture. Their underdeveloped gonads redirect energy from reproduction to muscle growth. This study compared embryonic development and antioxidant responses between allotriploid and hybrid diploid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) after cold shock, aiming to support large-scale allotriploid production. The diploid group had a 99.08% fertilization rate and 82.87% hatching rate, while the triploid group had lower rates (95.71% fertilization, 39.63% hatching, 11.52% deformity). Triploids developed later, with higher incidences of abnormalities and mortality, especially in the gastrula and neuro-embryo stages. Triploid larvae exhibited shortened tails, abnormal yolk sacs, and impaired swimming. Flow cytometry showed triploids that had 1.55 times more DNA and larger red blood cells. Triploids had lower midgut trypsin and lipase levels than diploids (p < 0.05) but similar glucose, liver malondialdehyde, and total cholesterol levels (p > 0.05). However, they had higher liver and spleen lactate dehydrogenase, catalase, and alkaline phosphatase, along with lower spleen malondialdehyde and liver superoxide dismutase (p < 0.05). These findings offer insights into reducing mortality in allotriploid grouper aquaculture, aiding large-scale production efforts. Full article

This study examined the diversity and responses of intestinal microbiota in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) fed diets with varying levels of fishmeal replaced by black soldier fly larvae (BSFL). The 10% BSFL substitution (BSFL10) group showed the highest levels of trypsin and amylase. Substituting fishmeal with 30% and 50% BSFL weakened the intestinal wall, resulting in vacuoles, sparse striatal boundaries, and fewer villi. Microbiota diversity, measured through Shannon’s index, was higher in the BSFL10 and BSFL50 groups than in the control. 16S rRNA amplicon data revealed the dominance of Firmicutes, Proteobacteria, Bacteroidetes, Spirochaetota, and Verrucomicrobia phyla. The BSFL-replacement groups showed an increase in Proteobacteria, Bacteroidetes, and Spirochaetota compared to the control, but fewer Firmicutes. PICRUSt analysis indicated significant alterations in microbial function, particularly enhanced protein, carbohydrate, lipid, and energy metabolisms in the BSFL-fed group. Substituting 10% fishmeal with BSFL enhanced nutrient metabolism and gut microbiota in juvenile hybrid grouper. Further research is needed to explore factors affecting the efficacy of insect feed as a sustainable aquaculture diet. Full article

Live fish transportation plays a crucial role in the commercial fish trade. Consequently, mitigating stress during transportation is essential for enhancing the survival rate of fish and reducing potential financial losses. In this study, the effectiveness was evaluated of exogenous tryptophan in reducing transport stress in hybrid grouper, Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂. Firstly, the groupers were divided into the following five experimental groups: 40 mg/L MS-222 group, 30 mg/L tryptophan, 50 mg/L tryptophan, 70 mg/L tryptophan, and the control group without additives. Followed by transportation simulation, the fish samples were collected before and after transportation for the determination of antioxidant enzyme activities, apoptosis gene, and inflammatory gene expressions. The results indicated that the superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities and malondialdehyde (MDA) levels in all groups were significantly increased, while they were lower in the 50 mg/L Trp treated group compared to the control group (p < 0.05). Compared with the control group in the 50 mg/L Trp, 70 mg/L Trp, and 40 mg/L MS-222-treated groups, serum cortisol and blood glucose levels were significantly increased (p < 0.05), and anti-inflammatory factor (IL-10) gene expression was upregulated and pro-inflammatory factor (IL-1β) gene expression was decreased (p < 0.05). In addition, it was found that the 30 mg/L Trp, 50 mg/L Trp, and 40 mg/L MS-222 treatment groups had less green fluorescence than the control group by measuring the mitochondrial membrane potential, and 50 mg/L Trp and MS-222 showed more red fluorescence in fluorescence images than the other samples at the same sampling time. Therefore, in this study, it was demonstrated that the tryptophan could be used as a new anti-stress agent for hybrid groupers during transport, and additional research is required to identify the specific conditions that yield the best outcomes. Full article

Vibrio harveyi is an important pathogen causing enteritis in hybrid groupers. However, its effects on the intestinal microbiota and the regulatory effects of oligochitosan on Vibrio-infected groupers are unclear. In this study, we investigated the effects of infection with V. harveyi and oligochitosan administration on the growth performance, immune responses, and intestinal transcriptome profiles of hybrid groupers during a 60-day rearing period. Growth parameters were reduced in Vibrio-infected groupers, while oligochitosan improved the body weight. Biochemical analysis showed reduced antioxidant enzyme activity and increased lipid peroxidation in Vibrio-infected groupers, which were consequently improved by oligochitosan. Transcriptome analysis was used to identify differentially expressed genes in the disease-related and immune system pathways that significantly accumulated in the treatment groups. An evaluation of the immune response showed a significant down-regulation of proinflammatory cytokines, antioxidant genes, and tight-junction proteins in Vibrio-infected groupers, which was partially restored by oligochitosan. Additionally, intestinal apoptosis, indicated by TUNEL signaling, was observed to significantly increase in Vibrio-infected groupers and was subsequently alleviated by oligochitosan supplementation. These results demonstrate the detrimental effects of V. harveyi infection on the growth and immune function of hybrid groupers and the potential of oligochitosan to attenuate these effects. Full article

Vibriosis caused by Vibrio vulnificus is a major problem in aquatic animals, particularly brown marble groupers (Epinephelus fuscoguttatus). V. vulnificus biotype I has recently been isolated and classified into subgroups SUKU_G1, SUKU_G2, and SUKU_G3 according to the different types of virulence genes. In a previous study, we have shown that biotype I V. vulnificus strains were classified into three subgroups according to the different types of virulence genes, which exhibited different phenotypes in terms of growth rate and virulence. To gain insight into the different genetic features revealed by the potential virulence mechanisms of V. vulnificus in relation to a spectrum of pathogenesis, comparative genomic analyses of three biotype I V. vulnificus strains belonging to different subgroups (SUKU_G1, SUKU_G2, and SUKU_G3) were performed. The V. vulnificus genome is composed of two circular chromosomes with average sizes of 3 Mbp and 1.7 Mbp that are evolutionarily related based on the analysis of orthologous genes. A comparative genome analysis of V. vulnificus revealed 5200 coding sequences, of which 3887 represented the core genome and the remaining 1313 constituted the dispensable genome. The most virulent isolate (SUKU_G1) carries unique enzymes that are important for lipopolysaccharide (LPS) and capsular polysaccharide (CPS) synthesis, as well as flagellar glycosylation, and harbors another type of repeat in toxin (RTX) and bacterial defense mechanisms. The less virulent isolate (SUKU_G2) shares enzymes related to CPS biosynthesis or flagellar glycosylation, while the avirulent isolate (SUKU_G3) and a less virulent isolate (SUKU_G2) share enzymes related to the production of rare sugars. Interestingly, the isolates from the three subgroups containing specific CMP-N-acetylneuraminate-producing enzymes that are correlated with their growth abilities. Collectively, these observations provide an understanding of the molecular mechanisms underlying disease pathogenesis and support the development of strategies for bacterial disease prevention and control. Full article

Pseudomonas plecoglossicida infection, which causes visceral white spot disease, is a significant and economically devastating disease in aquaculture. In this study, we investigated the impact of bacterial infection on the protein composition of exosomes derived from the surface mucus of the hybrid grouper Epinephelus fuscoguttatus♀ × E. lanceolatus♂. Two hundred healthy fish were randomly separated into challenge and control groups. Fish from the challenge group received 10³ CFU/g of the bacterial pathogen P. plecoglossicida via intraperitoneal injection, while sterile PBS was used as a negative control. After injection, the mucus was collected and the exosomes were extracted for proteomic analysis. The results of proteomic analysis revealed that P. plecoglossicida infection significantly increased the levels of innate immune proteins, including lysosomal and peroxisomal proteins, within the exosomes. Furthermore, the CAD protein was found to play a pivotal role in the protein interaction networks involved in the response to P. plecoglossicida infection. Intriguingly, we also observed a significant increase in the levels of metal-binding proteins within the exosomes, providing important evidence of nutritional immunity on the surfaces of the fish hosts. Notably, several proteins, such as plasma kallikrein, Annexin A5, eukaryotic translation initiation factor 3 subunit M, and S-methyl-5-thioadenosine phosphorylase, exhibited a remarkable increase in abundance in exosomes after infection. These proteins show promising potential as noninvasive biomarkers for the diagnosis of visceral white spot disease. The study contributes to the understanding of the host response to P. plecoglossicida infection and may aid policymakers in implementing appropriate intervention measures for effective risk management of this devastating disease. Full article

Aquafeed kept at elevated temperatures and humidity can result in malondialdehyde (MDA) formation, adversely affecting aquafeed quality and triggering negative reactions in fish. To investigate the detrimental effects of dietary MDA on fish, six experimental diets with varying MDA levels (ranging from 0.03 to 17.72 mg/kg, on dietary crude lipid basis) were administered to three replicates of hybrid grouper for 8 weeks. Dietary inclusion of 4.43 mg/kg MDA significantly decreased serum complement 4 content and lysozyme activity, along with intestinal complement 3, complement 4, and immunoglobulin M contents. Furthermore, dietary inclusion of 8.86 mg/kg MDA significantly increased the activities of interleukin-1 receptor-associated kinase, ubiquitin-protein ligase, p38 mitogen-activated protein kinase, and tumor necrosis factor-α, downregulated the relative expression of Occludin but upregulated the relative expression of HSP70 in the hindgut. Additionally, the highest inclusion of MDA (17.72 mg/kg) significantly upregulated the relative levels of pro-inflammatory cytokines (IL-1β and TNF-α), caused intestinal inflammation, and damaged the intestinal microbial structure and fish fillet texture. This study demonstrated a dose-dependent response of MDA on hybrid grouper. A low dietary dose of MDA (<2.21 mg/kg) exhibited minimal impact on immune response and fillet quality. However, higher inclusion levels (≥4.43 mg/kg) impaired the intestinal health and fillet quality. Consequently, the safety limit for MDA content in the diet for hybrid grouper has been established at 4.43 mg/kg based on dietary crude lipid basis. Full article

Vibrio harveyi is a major bacterial pathogen that causes disease in aquaculture animals worldwide. Although V. harveyi consistently harbors a range of traditional virulence genes, it remains unclear which specific genes are crucial for virulence at different infection stages. Dual RNA-seq is a cutting-edge RNA sequencing technology that is ideal for investigating the gene expression patterns of pathogens within the host, which is highly effective in identifying key virulence genes. In previous artificial infection experiments, we have identified the liver of hybrid grouper (♀ Epinephelus polyphekadion × ♂ E. fuscoguttatus) as the main target organ for pathogenic V. harveyi GDH11385 during the initial infection phase. To further explore the key virulence factors of V. harveyi at the early stage of infection, the liver of the hybrid grouper infected with strain GDH11385 was analyzed here by dual RNA-seq. The transcriptome data were compared with that of in vitro cultured bacteria. The results showed that 326 and 1140 DEGs (differentially expressed genes) were significantly up- and down-regulated, respectively, at 4 h post-infection (hpi). Further pathway enrichment analyses revealed that these up-regulated DEGs in vivo were mainly enriched in siderophore biosynthesis and transport, type VI secretion system (T6SS), flagellar assembly, glycolysis/gluconeogenesis, and ribosome. Notably, all genes involved in the metabolism and utilization of vibrioferrin (a carboxylate class of siderophore produced by Vibrio), and most of the genes within one of three T6SSs, were significantly up-regulated in vivo. This indicates that siderophore-dependent iron competition and T6SS-mediated delivery of virulence factors are vital for the successful colonization of V. harveyi at the early stage of infection. This study provides more precise clues to reveal the virulence mechanism of V. harveyi during the initial phase of infection. Full article

This study investigated the effect of substances on nonspecific immune responses of head kidney leukocytes, the antimicrobial activity against Vibrio sp., as well as the time-kill of Vibrio sp. by combining the substances with lactic acid bacteria (LAB) and Pediococcus sp. The substances are B. pilosa hot water extract, B. pilosa powder extract, B. pilosa methanol extract, B. pilosa ethanol extract, B. alba hot water extract, B. alba powder extract, B. alba methanol extract, B. alba ethanol extract, and bioactive compounds, namely cytopiloyne, flavonoid, phenol, ethyl caffeate, luteolin, chlorogenic acid, butein, and linoleic acid. The results showed that some of them were nontoxic to the head kidney leukocytes, which can increase the phagocytic rate, phagocytic index, and respiratory burst. These substances were able to inhibit the growth of Vibrio sp.; they can even completely kill the pathogenic bacteria. The largest of the inhibition zone formed from the EC group at a concentration range of 5–50 µg/mL against V. parahaemolyticus, V. alginolyticus, and V. harveyi with a value of 19.7 ± 0.56, 19.3 ± 1.53, and 20.6 ± 1.53 mm. Furthermore, the time-kill studies showed that the LAB and P. acidilactici can completely kill the Vibrio sp. at 6 h incubation time, mainly in the group of combination with EC. Full article

Poly-β-hydroxybutyrate (PHB) is a bacterial metabolite produced by bacteria such as Halomonas sp. that serves as a carbon and energy storage compound for bacteria under nutrient-limited conditions. Two experiments were conducted to investigate the effects of dietary supplementation with Halomonas-PHB on hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatu ♂). In experiment I, juvenile groupers were fed basal diets supplemented with 3% Halomonas-PHB (3% HM-PHB) containing 1.4% PHB and 3% Halomonas (3% HM) without PHB, as well as a control diet, for seven weeks. The results showed no significant difference in survival rate, weight gain, and crude fat content between the 3% HM-PHB group and the control group; however, the crude protein of the 3% HM-PHB group was significantly lower than that of the control group. Furthermore, supplementation with 3% HM-PHB increased the fatty acids content in fish muscles, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA. In experiment II, groupers were fed a basal diet supplemented with 6.5% Halomonas-PHB (6.5% HM-PHB) containing 3% PHB and 6.5% Halomonas (6.5% HM) containing no PHB, as well as a basal diet (Control). After seven weeks of rearing, the fish were challenged with Vibrio anguillarum for 48 h. Although no significant difference in survival rate and growth was observed among different groups, the dietary supplement of 6.5% Halomonas-PHB improved the survival rate of V. anguillarum challenged grouper and significantly increased the gene expressions of catalase (CAT) and superoxide dismutase (SOD) in blood, interleukin 1 (IL1) and interleukin 10 (IL10) in the liver, spleen, head kidney, and blood (p < 0.05). In conclusion, dietary supplementation of Halomonas-PHB had no significantly positive effect on fish growth performance but increased the content of fatty acids, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA in fish muscle; it also improved the V. anguillarum resistance, possibly through increasing immune-related gene expression in different tissues and organs. Our findings offer compelling evidence that Halomonas-PHB can be utilized as a feed additive in intensive grouper farming to enhance the groupers’ resistance to Vibrio. Full article