This study aimed to investigate the different regulatory mechanisms of euryhaline fish under regular hyperosmotic and extreme hyperosmotic stress. The OmB (Oreochromis mossambicus brain) cells were exposed to three treatments: control, regular hyperosmotic stress and extreme hyperosmotic stress. After 12 h exposure, proteomics, metabolomics analyses and integrative analyses were explored.Both kinds of stress lead to lowering cell growth and morphology changes, while under regular hyperosmotic stress, the up-regulated processes related with compatible organic osmolytes synthesis are crucial strategy for the euryhaline fish cell line to survive; On the other hand, under extreme hyperosmotic stress, the processes related with cell apoptosis and cell cycle arrest are dominant. Furthermore, down-regulated pyrimidine metabolism and several ribosomal proteins partially participated in the lowered cell metabolism and increased cell death under both kinds of hyperosmotic stress. The PI3K-Akt and p53 signaling pathways were involved in the stagnant stage of cell cycles and induction of cell apoptosis under both kinds of hyperosmotic stress. However, HIF-1, FoxO, JAK-STAT and Hippo signaling pathways mainly contribute to disrupting the cell cycle, metabolism and induction of cell apoptosis under extreme hyperosmotic stress. Significance In the past, the research on fish osmoregulation mainly focused on the transcription factors and ion transporters of osmoregulation, the processes between osmotic sensing and signal transduction, and the associations between signaling pathways and regulation processes have been poorly understood.Investigating fish cell osmoregulation and potential signal transduction pathways is necessary. With the advancements in omics research, it is now feasible to investigate the relationship between environmental stress and molecular responses.In this study, we aimed to explore the signaling pathways and substance metabolism mode during hyper-osmoregulation in OmB cell line, to reveal the key factors that are critical to cell osmoregulation.

This research explores the influence of myo-inositol (MI) on the hypertonic stress adaptation of Nile tilapia (Oreochromis niloticus) by increasing lipid utilization under long-term salinity stress. A two-factor interactive experiment was used, and diets containing either normal lipids (NL, 7%) or high lipids (HL, 15%) contained three MI concentrations of 0, 400, and 1200 mg/kg in each lipid diet. Fish were fed six diets under 20 psu (practical salinity units [psu]) for eight weeks. Under long-term hypertonic stress, dietary MI supplementation significantly improved the growth per-formance of O. niloticus (P < 0.05). Dietary 1200 mg/kg MI supplementation significantly pro-moted protein deposition and reduced fat accumulation in the whole fish (P < 0.05). The HL diet significantly caused lipid accumulation in the liver, while dietary 1200 mg/kg MI addition alleviated lipid accumulation by promoting the expression of genes related to lipolysis (PPAR-alpha; ATGL and CPT) and inhibiting the expression of genes related to lipid synthesis (SREBP; DGAT and FAS) (P < 0.05). In addition, 400 mg/kg MI significantly reduced serum lipids (TG and LDL-C) (P < 0.05). qPCR showed that the purity of dietary 1200 mg/kg MI significantly upregulated the expression of an ion transporter-related gene (NKA) in gills (P < 0.05). Meanwhile, 400 mg/ kg and 1200 mg/kg MI significantly affected the content of fatty acids in the liver and gill (P < 0.05). In addition, dietary 1200 mg/kg MI supplementation significantly increased the antioxidant capacity in the liver of O. niloticus. In conclusion, dietary supplementation with 1200 mg/kg MI could regulate lipid metabolism, promote lipid utilization and improve the osmotic regulation ability of O. niloticus.

The purpose of this study was to explore the relationship between inositol metabolism and carbohydrate metabolism in Nile tilapia (Oreochromis niloticus) under acute hyperosmotic stress. 50 mg/mL glucose solution and PBS was injected to the fish of experimental group and the control group, respectively. The fish were then transferred to 16 psu brackish water for hyperosmotic stress immediately, and sampled at 0, 1, 3, 6, 12, 24, and 48 h post stress. The hyperosmotic stress significantly increased the osmotic pressure, glucose content of serum, the process of glycolysis and gluconeogenesis in the liver of fish in both groups over time. The expression of genes involved in myo-inositol (MI) synthesis and transport was all induced by hypertonicity in gill, kidney and liver of fish in both groups. The injection of glucose solution significantly decreased MI synthesis in gill, kidney and liver, and relieved the apoptosis of liver under acute hyperosmotic stress. However, glucose injection significantly increased Na+K+-ATPase activity in the gill, as well as serum osmotic pressure, and the decomposition of carbohydrate, indicating that additional glucose promoted osmoregulation ability of fish. The results of this research suggested that during the hyperosmotic stress, the injection of exogenous glucose could not only provide energy that required for osmoregulation, but also participate in the osmoregulation by acting as an osmolyte itself.

A two-factor (2 x 3) orthogonal test was conducted to investigate the effects of dietary myo-inositol (MI) on the osmoregulation and carbohydrate metabolism of euryhaline fish tilapia (Oreochromis niloticus) under sustained hypertonic stress (20 practical salinity units [psu]). 6 diets containing either normal carbohydrate (NC, 30%) or high carbohydrate (HC, 45%) levels, with 3 levels (0, 400 and 1,200 mg/kg diet) of MI, respectively, were fed to 540 fish under 20 psu for 8 weeks. Dietary MI supplementation significantly improved growth performance and crude protein content of whole fish, and decreased the content of crude lipid of whole fish (P < 0.05). Curled, disordered gill lamella and cracked gill filament cartilage were observed in the gill of fish fed diets without MI supplementation. The ion transport capacity in gill was significantly improved in the 1,200 mg/kg MI supplementation groups compared with the 0 mg/kg MI groups (P < 0.05). Moreover, the contents of Na??, K??, Cl in serum were markedly reduced with the dietary MI supplementation (P < 0.05). The fish fed 1,200 mg/kg MI supplementation had the highest MI content in the gills and the lowest MI content in the serum (P < 0.05). Additionally, the fish fed with 1,200 mg/kg MI supplementation had the highest MI synthesis capacity in gills and brain (P < 0.05). Dietary MI markedly promoted the ability of carbohydrate metabolism in liver (P < 0.05). Moreover, fish in the 1,200 mg/kg MI groups had the highest antioxidant capacity (P < 0.05). This study indicated that high dietary carbohydrate would intensify stress, and impair the ability of osmoregulation in tilapia under a long-term hypersaline exposure. The supplementation of MI at 1,200 mg/kg in the high carbohydrate diet could promote carbohydrate utilization and improve the osmoregulation capacity of tilapia under long-term hypertonic stress. ?? 2022 Chinese Association of Animal Science and Veterinary Medicine. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC

Myo-inositol (MI) as a major intracellular osmolyte can be accumulated to protect cells from a variety of stress. The present study was to evaluate the effects of dietary MI on growth, osmotic response and transcriptional response in the liver of euryhaline fish Oreochromis mossambicus under long-term salinity stress. Five isonitrogenous and isolipidic diets were formulated to include 0 (MI0), 200 (MI200), 400 (MI400), 800 (MI800) and 1600 (MI1600) mg/kg MI. In this study, dietary 400 mg/kg MI significantly increased the weight gain and specific growth rate of O. mossambicus compared with the group without dietary MI supplementation under salinity stress. Moreover, dietary MI decreased serum glucose and insulin levels of fish under long-term salinity stress. Fish fed 400 mg/kg MI supplementation had significantly higher serum cortisol, sodium (Na+) and chloride ion (Cl-) than those fed a diet without MI supplementation. A total of 132.17 million and 115.8 million clean reads were obtained from the 0 mg/kg MI (MI0) and 400 mg/kg (MI400) MI group respectively. Compared with the MI0 group, the expression of 704 genes was significantly changed (521-up and 183-down) in the MI400 group under long-term salinity stress. Transcriptome results indicate that myo-inositol can regulate lipid and pyruvic acid metabolism, increase phospholipid synthesis-related mRNA levels and improve antioxidant properties of O. mossambicus under long-term salinity stress. This study suggests that optimum MI supplementation is 400 mg/kg in the diet based on weight gain against dietary MI and this result provides a nutritional solution for tilapia to cope with salinity stress.

This study was to evaluate the relationship between myo-inositol synthesis and carbohydrate metabolism in Mozambique tilapia (Oreochromis mossambicus). Fish were immediately transferred from 0 psu (practical salinity units, the control) to 20 psu for 96 h with 60 fish in each group. Compared with the control group, the volume of the mitochondria-rich cell in the gills of O. mossambicus was significantly increased by acute hypersaline stress. The osmotic pressure and the contents of Na+, K+ and Cl- in the serum were significantly increased in the 20 psu group. Moreover, fish in the 20 psu group had significantly higher activities of glutathione peroxidase and superoxide dismutase and a higher malondialdehyde content than the control in the liver. Salinity stress significantly increased the serum glucose but decreased the liver glycogen. The activities of glucokinase and phosphofructokinase in the liver and gills were significantly higher in the 20 psu group, indicating that glycolysis could be significantly enhanced by salinity stress. The activities of glucose-6-phosphate synthase and phosphoenolpyruvate carboxykinase in the liver were significantly decreased by salinity stress. The expressions of myo-inositol-1-phosphate synthase and myo-inositol monophosphatase were significantly up-regulated in the gills and kidney. However, the expressions of these two genes were significantly down-regulated in the liver. The myo-inositol content in the gills, kidney and liver in the 20 psu group were significantly increased by salinity stress. This study indicates that salinity stress can impair the gill structure and reduce the antioxidant capacity of O. mossambicus. The changes in MI biosynthesis and carbohydrate metabolism could be an effective strategy to alleviate the adverse effect of salinity stress.

Microplastics (MPs) coexist with other pollutants (such as heavy metals) in water, adversely impacting aquatic organisms, which might cause unpredictable ecological risks. This study aims to evaluate the effect of copper (Cu2+) and polystyrene microplastics (PS-MPs) on antioxidant capacity, immune response and intestinal microbiota of Nile tilapia. Cu2+ and PS-MPs co-exposure enhanced Cu2+ bioaccumulation in the liver of fish compared with Cu2+-alone exposure. Fish exposed to PS-MPs and Cu2+ displayed histopathologic alterations in the liver, intestine and gill. Exposure at low concentrations of Cu2+ in the C0 and CP0 groups can improve antioxidant capacity and immune response, while oxidative damage and inflammation existed in the high concentration of Cu2+ groups. Intestinal microbiota results showed that the diversity and structure were changed by Cu2+ and PS-MPs exposure, and harmful bacterium even increased at high concentration of Cu2+ and PS-MPs exposure groups. All in all, PS-MPs aggravate the accumulation of Cu2+ and lead to perturbations in biological systems of Nile tilapia.

This study evaluated the effects of dietary myo-inositol (MI) levels on growth, body composition, antioxidant status, non-specific immunity and lipid metabolism in juvenile Chinese mitten crab (Eriocheir sinensis). A total of 960 crabs was fed with six diets supplemented with graded levels of MI (0, 204, 406, 810, 1,650 and 3,211 mg/kg) for 8 weeks. The crabs fed with diets containing 1,650 mg/kg MI had significantly higher final body weight, weight gain and specific growth rate than those fed 0, 204, 406 and 810 mg/kg MI (p < .05). The lowest moulting frequency was observed in the crabs fed diets without supplemented MI. The crabs fed with diets containing 1,650 and 3,211 mg/kg MI had significantly lower total lipid content in the whole body than those fed diets without supplemented MI (p < .05). The myo-inositol level in hepatopancreas increased with increasing dietary MI up to 1,650 mg/kg before reaching plateau. The crabs fed 1,650 mg/kg MI had significantly higher total antioxidant capacity and glutathione peroxidase activity in hepatopancreas than those fed diets without supplemented MI (p < .05). However, the crabs fed diets without supplemented MI had the highest level of malondialdehyde in hepatopancreas compared with those fed with MI supplementation. The highest serum alkaline phosphatase activity was also observed in crabs fed 1,650 mg/kg MI. Total protein and haemocyanin contents in serum were significantly increased with increasing dietary MI levels (p < .05). The triglyceride contents in hepatopancreas significantly decreased with increasing dietary MI levels (p < .05). Results of real-time quantitative PCR revealed that dietary MI reduced hepatic triglyceride accumulation probably through inhibiting lipid synthesis-related genes and promoting lipid export-related genes at the transcriptional level. Broken-line analysis of weight gain, specific growth rate and MI levels in hepatopancreas against dietary MI levels indicates that the optimal MI requirement for juvenile crabs ranged from 1,613 to 1,707 mg/kg. The dietary MI supplementation can improve growth performance, antioxidant capacity and non-specific immunity and reduce hepatopancreatic triglyceride accumulation in juvenile crab.

This study investigated the effect of dietary myo-inositol (MI) on alleviating the adverse effect of the high carbohydrate diet in Nile tilapia (Oreochromis niloticus). Six diets contained either low carbohydrate (LC 30%) or high carbohydrate (HC 45%) with three levels of MI supplementation (0, 400 and 1200 mg/kg diet) to each level of the carbohydrate diet. After an 8-week trial, the fish fed 400 mg/kg MI under HC levels had the highest weight gain and fatness, but the fish fed 1200 mg/kg MI had the lowest hepatosomatic index, visceral index and crude lipid in the HC group. The diet of 1200 mg/kg MI significantly decreased triglyceride content in the serum and liver compared with those fed the MI supplemented diets regardless of carbohydrate levels. Dietary MI decreased triglyceride accumulation in the liver irrespective of carbohydrate levels. The content of malondialdehyde decreased with increasing dietary MI at both carbohydrate levels. Fish fed 1200 mg/kg MI had the highest glutathione peroxidase, superoxide dismutase, aspartate aminotransferase and glutamic-pyruvic transaminase activities. The HC diet increased the mRNA expression of key genes involved in lipid synthesis (DGAT, SREBP, FAS) in the fish fed the diet without MI supplementation. Dietary MI significantly under expressed fatty acid synthetase in fish fed the HC diets. Moreover, the mRNA expression of genes related to lipid catabolism (CPT, ATGL, PPAR-α) was significantly up-regulated with the increase of dietary MI levels despite dietary carbohydrate levels. The gene expressions of gluconeogenesis, glycolysis and MI biosynthesis were significantly down-regulated, while the expression of the pentose phosphate pathway was up-regulated with the increase of MI levels. This study indicates that HC diets can interrupt normal lipid metabolism and tend to form a fatty liver in fish. Dietary MI supplement can alleviate lipid accumulation in the liver by diverging some glucose metabolism into the pentose phosphate pathway and enhance the antioxidant capacity in O. niloticus.