Jian-dong Zhang’s research while affiliated with Guangdong Ocean University and other places

Nutrition, disease, and general wellbeing can be affected by the microbial communities associated with the digestive tracts of aquaculture species. Different sections of aquaculture species’ digestive tracts have distinctive surfaces and structures, which can change microbial communities. The present study examined the composition and distribution of bacterial species in the intestine of hybrid grouper (Epinephelus fuscoguttatus E. polyphekadion) and its aquaculture environment. Using high-throughput pyrosequencing, a 16S rRNA sequence analysis was performed on hybrid grouper foregut, midgut, and hindgut, as well as cultured water and feed. There were 610,452 sequences obtained from five components (foregut, midgut, hindgut, water, and feed). Among operational taxa (OTUs), 506 of them were detected in the foregut, 605 in the midgut, 510 in the hindgut, and 573 in aquaculture water and feed samples. A total of 113 were detected in 5 samples. A species annotation revealed that hybrid grouper intestinal tracts were dominated by Proteobacteria (67.3%–73.7%), Firmicutes (8.4%–14.0%), and Actinobacteria (6.9%–10.5%). In aquaculture culture water, Proteobacteria were predominant (36.3%), Actinobacteria (30.0%), and Planctomycetes (14.0%). Acinetobacter (1.4%–17.9%) and Photobacterium (32.0%–57.5%) dominated the intestine. Photobacterium (3.6%) and Mycobacterium (7.1%) dominated the water bacteria. The water and intestine contained five potentially pathogenic bacteria: Pseudomonas, Flavobacterium, Escherichia coli, Aeromonas bacteria, and Vibrio. The highest proportion of Vibrio was found in the water (1.7%), while Pseudomonas dominated the midgut (2.6%). Six potential probiotics were detected in the aquaculture water and intestine (Lactococcus, Streptococcus, Bdellovibrio, Lactobacillus, Bacillus, and Bacteroides). Aquaculture water and intestines contained Bacillus, Bacteroides, and Lactobacillus. According to the findings, the intestinal flora of hybrid grouper is closely correlated with its pond culture environment. Results from the study provide an experimental basis for the controlled breeding of hybrid groupers and the regulation of their microecological processes in the breeding environment deepen our understanding of the intestinal bacterial population of healthy hybrid groupers.

Cobia is an important cultured marine fish species in southern China. It is characterised by fast growth. Due to the effects of climate change on water oxygen levels and seawater temperatures, understanding the influence of environmental challenges on cobia culture has become very important. In this study, to explore the stress and adaptability of cobia (Rachycentron canadum) during hypoxia-reoxygenation conditions, the fish were exposed to an oxygen-deficient environment with dissolved oxygen (DO) level of 2.64 ± 0.25 mg/L. Liver tissue transcriptome sequencing was detected in the fish at acute hypoxia stress, after which fish were returned to normal DO levels (6.34 mg/L) for 8, 24, and 48 h. Comparative analysis of liver transcriptomes revealed that there were 1689, 651, 236, and 1150 differential genes in the hypoxia stress group (SC), reoxygenation-8h group (R8), reoxygenation-24h group (R24), and reoxygenation-48h group (R48), respectively. The differentially expressed genes were compared with the GO database. The main aggregated genes were related to gene ontology functional elements such as ribosome structural components, matrix-dependent cell migration, hormone activity, and oxidoreductase activity. The differentially expressed genes were compared with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and a total of 43,054 differentially expressed genes were found to be enriched in 212 cases. For the first time, gene expression patterns in the liver of a juvenile’s cobia were examined in response to hypoxia. The results of this study contribute to further clarifying hypoxia’s effects on the liver of marine fish.

An estimation of the utilization of endogenous nutrients from the yolk sac that occurs during embryonic and early larval development can be a valuable approach to studying the nutritional requirements of fish larvae. In this study, fertilized eggs, embryos (before the membrane, 24 hours after fertilization), newly-hatched larvae (0-d-old), and open-mouthed larvae (3-day-old, unfed rotifers) samples of cobia (Rachycentron canadum) were collected to determine the amino acid and fatty acid profiles. Crude protein composition varies significantly for cobia during the different stages of development. The total amino acids, except for lysine(Lys), histidine (His), methionine(Met), serine(Ser), and glycine(Gly), had no significant change in the early development stage (P > 0.05); the content of other six essential amino acids (EAA) and six non-essential amino acids (NEAA) was consistent with the changing trend of total essential amino acid. From hatching newly hatched larvae to open-mouthed larvae, except for Leu, Phe and Ser, decreased significantly (P<0.05). From the utilization rate of FAA, the utilization rate of Lys and Leu was the highest (60.26%) and (52.21%) in the embryonic and endogenous nutritional stages, respectively. The water content of the open-mouthed larvae of cobia was significantly higher than that of the fertilized eggs, embryos, and newly hatched larvae (P < 0.05). Three kinds of saturated fatty acids (SFA), five kinds of monounsaturated fatty acids (MUFA), and eight kinds of polyunsaturated fatty acids (PUFA) were detected in the dry samples of each developmental stage. Based on these results, juvenile cobia can thrive with a wide range of crude protein concentrations. Further refinement of commercial cobia production feeds would have beneficial consequences for economic and environmental concerns due to the positive impacts of optimizing the protein component as well as the ability to maintain the rapid growth rates. The results show that the larval development of cobia needs to consume large amounts of n3PUFA (especially DHA and EPA) to improve the larvae’s survival rate. Research methods will always have limitations when evaluating the relationship between early life nutrition interventions and well-being outcomes later in life. This study provides essential information regarding cobia larvae’s fatty acid requirements.

In intensive aquaculture systems, dissolved oxygen (DO) is the most critical and limiting factor for the development and health of aquatic organisms. Hypoxia is a common phenomenon in aquaculture. Its effects on fish’s growth and immune system have been widely reported, but the molecular mechanisms of hypoxic stress on damage to the fish gut are not fully understood. Additionally, studies on the effects of hypoxic stress on the intestinal metabolism of cobia (Rachycentron canadum) are still limited. Therefore, this study used cobia to explore the effects of hypoxic stress on intestinal metabolism. In this study, the combination of high-throughput RNA sequencing (RNA-Seq) and non-targeted liquid chromatography-mass spectrometry (LC-MS) based metabolomics analyses were used to investigate changes in key genes and metabolites in the intestinal tract of juvenile cobia after 28 days of hypoxic stress (DO: 3.15 ± 0.21 mg/L). Transcriptomics analysis revealed the significant enrichment of 62 metabolic pathways, including glutathione metabolism, fat digestion and absorption, bile secretion, glycerolipid metabolism, tricarboxylic acid cycle, glycolysis/gluconeogenesis, and other pathways. Metabolomics analysis revealed that most of the significantly differential metabolites were related to the metabolism of amino acids and lipids. The combined transcriptomics and metabolomics analyses showed that the sustained hypoxic stress could cause some degree of oxidative damage to the gut of cobia, thereby interfering with its digestive absorption and physiological and metabolic processes, such as abnormalities in antioxidant and detoxification functions, disturbances in the metabolisms of amino acids, lipids, and carbohydrates, and reduction of ion transport capacity. These findings might help understand the molecular mechanisms of the intestinal tract under hypoxic stress in cobia, thereby reducing the damage caused by hypoxic stress to farmed fish.

In this study, cobia (Rachycentron canadum) juveniles were utilised as an aquatic model to explore growth performance and immune indices after 70 days of feeding with supplementation of viable isolated microbes’ concentrations of 1 × 10¹⁰ and 1 × 10¹² CFU/mL indigenous isolates Bacillus sp. RCS1 and Bacillus cereus strain RCS3, respectively. Regarding growth performance, fish provided with the indigenous isolates exhibited a significant (P < 0.05) enhancement. The hematological indices such as red blood cells, white blood cells, corpuscular haemoglobin concentration, mean corpuscular volume, haemoglobin, and Mean corpuscular haemoglobin were all increased (P < 0.05) in the juvenile cobia fed with indigenous isolates Bacillus sp. RCS1 and B. cereus RCS3 as a nutritional supplement. This study also significantly differed in serum analysis (albumin, globulin, lysozyme, total protein) between all the treatments with the Bacillus sp. RCS1 1 × 10¹⁰ proven to be the best. In the present study, the expression of myostatin and insulin-like growth factor 2 showed no significant change (P > 0.05) among the treatment and control groups tested; nonetheless, their mRNA expression exhibited variations in all trial groups. The present study showed significant differences (P < 0.05) among groups in the case of insulin-like growth factor 1, peroxisome proliferator-activated receptors. The improved antioxidant enzyme activities of catalase (CAT) and superoxide dismutase (SOD) digestive enzyme activities (amylase, trypsin, pepsin, lipase, and cellulose) may be linked to the enhanced resistance of fish against Vibrio harveyi infection. The enhanced activities of digestive enzymes in indigenous isolates treatments could be linked to the improved digestion and enhanced food absorption that ultimately helps enhance feed utilisation and growth performance. The results showed that indigenous isolates addition to a commercial diet, had the prospective to enhance cobia juveniles' growth and immune response regardless of their dosage.

Hypoxia is a lack of required oxygen to meet the metabolic demands of living organisms. Cellular hypoxia occurs when the molecular oxygen, essential to maintain sufficient adenosine triphosphate (ATP) levels for normal physiological function, surpasses the vascular supply. Tissue hypoxia can arise during a range of diseases. As molecular oxygen is a crucial metabolic energy source for all living organisms, animals manage the intracellular oxygen levels to sustain homeostasis, with the upregulation of genes that improve tissue perfusion and anaerobic ATP creation via glycolysis. This is facilitated by the hypoxia-inducible factors (HIFs). Hypoxia-inducible factor 1α (hif-1a) is the core regulator of the hypoxia response and plays a crucial role in the cellular/molecular response to hypoxic stress by regulating the transcription of target genes. In the present study, hif-1a cDNA was identified and cloned from cobia (Rachycentron canadum), using rapid amplification of cDNA ends (RACE). The hif-1a and downstream mRNA expression levels in various tissues were then determined. The full length of hif-1a cDNA is 3642 bp, with a 2292 bp open reading frame (ORF), a 5′ non-coding region (5′-UTR) of 293 bp, 3′ non-coding region (3′-UTR) of 1057 bp, and encoding 764 amino acids. The encoded protein contains the basic helix-loop-helix domain (amino acid 22–77), PER-Arnt-SIM domain (amino acid 88–154 and 230–296), and the PAS-associated C-terminal domain (amino acid 302–345). hif-1a mRNA expression was detected in nine tissues, with the highest expression observed in the liver, and the lowest expression in the intestine and spleen. hif-1a, erythropoietin (epo), and vascular endothelial growth factor (vegf) gene expressions were analyzed in the gill, intestine, liver, and muscle under hypoxic stress. In the gills, hif-1a expression was significantly increased at all hypoxia time points as well as in the liver. Erythropoietin (epo) and vascular endothelial growth factor (vegf) showed similar trends, with a significant decrease followed by a significant increase. In the muscle, the expression of all three genes was higher than the control group after hypoxic stress. These results indicate that the expression patterns of hif-1a and related genes after hypoxic stress are tissue-specific and play an essential role in cobia’s response to hypoxia.

At present, due to the influence of global warming, seasonal change, diurnal variation, and eutrophication of the water body, hypoxia has become one of the major factors limiting the stable development of cobia (Rachycentron canadum) culture. In this study, the miRNAs involved in hypoxia stress were screened, and the target genes of miRNAs were annotated and analyzed. The results showed that a total of 184 conservative microRNA (miRNA) and 121 newly predicted miRNA were obtained by sequencing the liver of control (C) and hypoxic (dissolved oxygen, DO (2.64 ± 0.25) mg/L; 3 h) (S) groups. The pathways involved in energy metabolism included starch and sucrose metabolism (ko00500), glycosaminoglycan degradation (ko00531), and galactose metabolism (ko00052). The results indicate that the body maintains physiological activities by regulating some important pathways at the transcriptional level under hypoxia stress, such as the conversion of aerobic metabolism and anaerobic metabolism, the reduction of energy consumption, and the promotion of red blood cell proliferation to maintain the homeostasis of the body.

Background Environmental hypoxia affects the survival and development of organisms. It is also an important environmental factor that leads to oxidative damage. Hypoxia is a condition in which tissues are deprived of oxygen; reoxygenation is the phenomenon in which hypoxic tissues are exposed to oxygen. Hypoxia-reoxygenation is vital in pathogenesis, where the production of reactive oxygen species and antioxidant disparity significantly contribute to disease progression, and it is one of the most common physiological stressors in the aquaculture industry.Methods and resultsIn this study, the full length of complementary DNA (cDNA) of the manganese superoxide dismutase (Mn-SOD) gene of healthy cobia Rachycentron canadum was analysed using rapid amplification of cDNA ends. The real-time quantitative Polymerase Chain Reaction was used to measure the expression levels of Mn-SOD mRNAs in various tissues (heart, muscle, brain, liver, kidney, gill, intestine, and spleen). The 2–ΔΔCT method was used to performed the expression analysis. The experimental data were analysed using SPSS ver. 19.0 (https://spss.software.informer.com/19.0/). P < 0.05 and P < 0.01 were set as significant differences. The values were articulated as mean ± standard deviation. The Mn-SOD gene cDNA sequence was 1209 bp long, including a 684 bp open reading frame, 42 bp 5'UTR and 483 bp 3'UTR, encoding 227 amino acids. Under hypoxia-reoxygen stress, the expression of Mn-SOD in brain tissue was significantly lower than in the control group after 8 h of reoxygenation and higher than the control group after 24 h. Hypoxia and subsequent reoxygenation triggered a disturbance in antioxidant homeostasis, displayed in the modification of GPx expression/activity in the liver: GPx was improved.Conclusions These results provide valuable information on the role of Mn-SOD regulation in oxidative stress caused by hypoxia.

Cobia (Rachycentron canadum) is an important cultured marine fish species in southern China. It is characterized by fast growth. Due to the effects of climate change on water oxygen levels and seawater temperatures, the understanding of the influence of environmental changes on cobia culture has become important. In this study, to explore the stress and adaptability of cobia under hypoxia-reoxygenation conditions, the fish were exposed to an oxygen-deficient environment with dissolved oxygen (DO) level of 2.64 ± 0.25 mg/L. Serum liver function target, lipid metabolism-related enzymes and the serum antioxidant capability were detected in cobia under acute hypoxic stress after which fish returned to normal DO level (6.34 ± 0.15 mg/L) at 8, 24 and 48 h. Conventional paraffin sectioning and hematoxylin and eosin (H-E) staining were used to observe gill and liver tissues of cobia by electron microscopy. After hypoxic stress, the activities of alkaline phosphatase (ALP), total protein (TP), albumin (ALB), triglyceride (TG), total cholesterol (TC) and superoxide dismutase (SOD) in cobia decreased. Under acute hypoxic stress, the gill patches of the fish were contracted and slightly curved. Liver disorder and vacuoles appeared between liver tissues. After reoxygenation, SOD and catalase (CAT) were recovered to the level of the control group with time, and all peaks appeared. The gill and liver of fish were also recovered with time. The results showed that hypoxic stress could cause oxidative damage to cobia.

In this study, juvenile cobia fish (Rachycentron canadum) (body weight: 50.44 ± 2.78 g) were used as a study object to investigate the effects of hypoxia stress (dissolved oxygen: 3.15 ± 0.21 mg/L) on the activities of their digestive enzymes, intestinal morphology and relative expression of tight junction proteins coding genes. Under the experimental conditions, the juvenile cobia were given 28 days of hypoxia stress. The results showed that the activities of digestive enzymes in the intestines of the hypoxia stress group decreased. In addition, the amylase and lipase activities decreased significantly (p < 0.05), and the trypsin activity in the hypoxia stress group compared to that in the control group. The morphology and structure of the intestine also showed significant changes. Under the microscopic observation, the mucosal fold height and muscle thickness of the intestine showed a significant decrease (p < 0.05); also, the villi's width showed a significant decrease (p < 0.05) in the hypoxia stress group as compared to that in the control group. The observation under a transmission electron microscope showed that the microvilli of juvenile cobia in the hypoxia stress group were irregularly arranged, atrophied and fallen off compared to the control group. Furthermore, there were gaps in the tight junction. In addition, the boundary between cells was unclear. The relative expression of intestinal tight junction proteins coding genes was down‐regulated to varying degrees. The mRNA expressions of ZO‐1 and claudin‐4 were significantly down‐regulated (p < 0.05) and ZO‐2 and occludin in the hypoxia stress group compared to those in the control group. These results indicated that hypoxia stress could inhibit the activities of intestinal digestive enzymes, damage intestinal morphology and decrease the expression of tight junction proteins coding genes in cobia. The present study provided a scientific foundation for evaluating the multifaceted impacts of hypoxia stress on fish species, such as cobia.