Interactive effect of thermal and hypoxia on largemouth bass (Micropterus salmoides) gill and liver: Aggravation of oxidative stress, inhibition of immunity and promotion of cell apoptosis.

High temperatures and low oxygen in aquatic environments, such as intensive aquaculture or in natural watersheds, inevitably cause stress in fish. Fish are exposed to high temperatures during the summer, which exacerbates hypoxia. Hypoxia (1.2 ± 0.2 mg/L) under 20 °C (20 HG) and 26 °C (26 HG) was simulated to induce stress in largemouth bass (Micropterus salmoides). Related enzymes and genes involved in antioxidant, immune, and apoptotic responses were selected to explore the interactive effects of temperature and hypoxia on largemouth bass. The results showed that malondialdehyde (MDA) levels in plasma, gill, and liver increased in the 26 HG (p < 0.05). Liver superoxide dismutase (SOD) activity increased in the 26 HG. Peak SOD (SOD1, SOD2, SOD3a, and SOD3b), CAT, and GSH-Px mRNA levels in the gill and liver were observed at 12-24 h of stress. The levels of gill and liver total antioxidant capacity, catalase (CAT), glutathione peroxidase (GSH-Px) activities and other enzyme activities and genes in the 26 HG were higher than those in the 20 HG (p < 0.05). The gill and liver acid phosphatase and alkaline phosphatase activities increased with time in the 26 HG (p < 0.05), while gill and liver lysozyme activities in the 26 HG were lower than those in the 20 HG (p < 0.05). Tumor necrosis factor-α mRNA level was upregulated in the gill and downregulated in the liver at 24 h in the 26 HG. Interleukin (IL)-1ß and IL-8 mRNA levels were upregulated in the gill and liver in the 26 HG at 24 h, whereas IL-15 mRNA level was downregulated in the 26 HG at 12 h. Transforming growth factor-ß1 mRNA level was upregulated in the gill in the 20 HG at 24 h, but downregulated in gill and liver in the 26 HG at 24 h. Similarly, IL-10, Hepcidin-1, and Hepcidin-2 showed lower expression levels in the 26 HG. Gill and liver caspase-3 activities were higher in the 26 HG (p < 0.05), and gill caspase-3 activity was higher than that in the liver. The mRNA levels of proapoptotic genes (caspase-3, caspase-8, and caspase-9) were higher in the 26 HG. The present study demonstrates the interactive effects of temperature and hypoxia on stress in largemouth bass gill and liver. These results will be helpful to understand the mechanisms of stress induced by temperature and hypoxia in fish and provide a theoretical basis for aquaculture management.

MicroRNA regulation in hypoxic environments: differential expression of microRNAs in the liver of largemouth bass (Micropterus salmoides).

Environmental changes in intensive aquaculture commonly lead to hypoxic stress for cultured largemouth bass (Micropterus salmoides). To better to understand the hypoxic stress response mechanisms, the miRNA expression profiles of the livers of largemouth bass exposed for 24 h to three different dissolved oxygen levels (7.0 ± 0.2 mg/L as control, 3.0 ± 0.2 mg/L and 1.2 ± 0.2 mg/L) were compared. In this study, a total of 266 known miRNAs were identified, 84 of which were differentially expressed compared with the control group. Thirteen of the differentially expressed miRNAs (miR-15b-5p, miR-30a-3p, miR-133a-3p, miR-19d-5p, miR-1288-3p, miR456, miR-96-5p, miR-23a-3p, miR-23b-5p, miR-214, miR-24, miR-20a-3p, and miR-2188-5p) were significantly enriched in VEGF signaling pathway, MAPK signaling pathway, and phosphatidylinositol signaling system. These miRNAs were significantly downregulated during stress, especially after a 4-h exposure to hypoxia. In contrast, their target genes (vegfa, pla2g4a, raf1a, pik3c2a, clam2a, inpp1, pi4k2b, mtmr14, ip6k, itpkca, map3k7, and Jun) were significant upregulated after 4 h of hypoxic stress. Moreover, two potential hypoxia-tolerance signal transduction pathways (MAPK signaling pathway and phosphatidylinositol signaling system) were revealed, both of which may play important roles in responding to acute hypoxic stress. We see that miRNAs played an important role in regulating gene expression related to physiological responses to hypoxia. Potential functional network regulated by miRNAs under hypoixic stress in the liver of largemouth bass (Micropterus salmoides). Blue boxes indicated that the expression of miRNA or target genes were down-regulated. Red boxes indicated that the expression of miRNA or target genes wasere up-regulated.

Influence of long-term temperature stress on respiration frequency, Na+/K+-ATPase activity, and lipid metabolism in common carp (Cyprinus carpio).

Temperature is a key factor that influences fish metabolism. Therefore, it is important to understand how temperature variation affects lipid metabolism and energy consumption in fish. We determined respiration frequency, Na+/K+-ATPase activity, and lipid metabolism in common carp (Cyprinus carpio) after 18 days of temperature stress (5 °C and 30 °C, with 17 °C as the control). We found that respiratory frequency was positively correlated with water temperature (p < 0.01), whereas red blood cell count and mean corpuscular hemoglobin content and concentration were negatively correlated with temperature. In liver and heart, triglyceride (TG) levels were lower in both stress groups (5 °C and 30 °C) than in the control (17 °C) (p < 0.01), and highest in muscle from the high temperature stress group (p < 0.01). The non-esterified fatty acid concentration was negatively correlated with TG levels. In brain, lipoprotein lipase (LPL) activity decreased with increasing temperature and hepatic lipase (HL) activity was lower in both stress groups than in the control (p < 0.01). In muscle, the activity of LPL and HL was lowest in the high temperature stress group, resulting in a significant increase in TG levels. Na+/K+-ATPase activity in heart was lower in both stress groups than in the control (p < 0.01). The expression of LPL mRNA in heart increased with increasing temperature (p < 0.01), whereas LPL mRNA expression in brain and liver increased in both stress groups (p < 0.01). Our results show that temperature can significantly affect lipid metabolism in common carp, and that different tissues respond differently to changes in temperature.

Differences in the digestive enzyme activity, intestinal mucosa and microbial community in loach cultivated in two separate environments.

BACKGROUND: Fish culture in rice paddies can contribute to increasing yields of rice and surplus fish products. Environmental impacts and food-safety issues have become important topics in aquaculture, and organic foods currently were paid attention by researchers and industry practitioners. But the mechanism of differences in quality of Loach (Paramisgurnus dabryanus) reared in rice fields and ponds remains largely uncharacterized. In this study,digestive enzyme activity, intestinal mucosa cells and the gut microbial community of loach were determined under the two separate cultivation modes. RESULTS: The levels of intestinal digestive enzyme activity of fish reared in the paddy-cultivated mode (PACM) were higher (P < 0.05) than those in the pond-cultivated mode (POCM). It was extremely significant (P < 0.01) for the activity of lipase in the liver, foregut and midgut, and for the activities of amylase and trypsin in the hindgut. Acid mucous cells in the loach foregut in PACM were fewer than in POCM (P < 0.01). In summer, the abundance of the Firmicutes, Lactobacillus spp., Aeromonas hydrophila, Enterobacteriaceae and Streptococcus spp. in loach intestinal mucosa in PACM was higher than in POCM. In fall, the abundance of total bacteria, the Bacteroidetes, Bifidobacterium and Enterobacteriaceae in the intestinal mucosa in PACM was likewise higher than in POCM. These differences were significant (P < 0.05 or P < 0.01) between loach in the two separate culture modes for all microorganisms except for A. hydrophila and Streptococcus spp. In addition, quantitative PCR assays showed that some microorganisms presented consistently similar abundances in the gut as in the culture water. CONCLUSIONS: These results showed some enzymatic activities involved in digestion in liver and intestine of loach in PACM were higher than those in POCM, as using digestive enzyme analysis and histological observation of intestinal sections. These findings suggest most of the microorganisms examined in the gut mucosa of loach in the two culture modes significantly differed in abundance between summer and fall. However, some pathogenic bacteria in the gut, particularly A. hydrophila, presented lower abundance in PACM in fall, yet did not differ in abundance between loach in the two cultivation modes.

Physiological responses to acute hypoxia in the liver of largemouth bass by alteration of mitochondrial function and Ca2+ exchange.

Oxygen is a critical factor for most organisms and this is especially true for aquatic animals. Unfortunately, high-density aquaculture farming practices and environmental degradation will inevitably lead to hypoxic stress in fishes such as largemouth bass (Micropterus salmoides). Thus, characterizing the physiological responses during acute hypoxia exposure is extremely important for understanding the adaptation mechanisms of largemouth bass to hypoxia. The present study aimed to investigate mitochondrial function and Ca2+ exchange in largemouth bass under hypoxic conditions. Largemouth bass were subjected to hypoxia (1.2 ± 0.2 mg/L) for 24 h Liver mitochondria and endoplasmic reticulum (ER) parameters were analyzed. We used Liquid chromatography-mass spectrometry (LC-MS) to further elucidate the pattern of energy metabolism. Changes of Ca2+ concentrations were observed in primary hepatocytes of largemouth bass under hypoxic conditions. Our results indicate that the morphology and function of the mitochondria and ER were altered under hypoxia. First, the occurrence of autophagy was accompanied by reactive oxygen species (ROS) generation and electron transport chain (ETC) activity modulation under hypoxia. Second, hypoxia enhanced mitochondrial fusion and fission, mitochondrial biosynthesis, and ER quality control in the early stages of hypoxic stress (before 8 h). Third, hypoxia modulated tricarboxylic acid (TCA) cycle flux and caused the accumulation of TCA intermediate metabolites (citric acid and oxoglutaric acid). Additionally, Ca2+ efflux in the ER was observed., and the genes for Ca2+ transporters presented high expression levels in cellular and mitochondrial membranes. Collectively, the above physiological responses of the mitochondria and ER contributed to maintaining energy production to withstand the hypoxic stress in largemouth bass. These results provide novel insights into the physiological and metabolic changes in largemouth bass under hypoxic conditions.

Acute hypoxia changes the mode of glucose and lipid utilization in the liver of the largemouth bass (Micropterus salmoides).

Dissolved oxygen (DO) undountedly affects fish distribution, metabolism, and evern survival. Intensive aquaculture and environmental changes will inevitably lead to hypoxic stress for largemouth bass (Micropterus salmoides). The different metabolic responses and mechanism still remains relatively unknown during acute hypoxia exposure. In this study, largemouth bass were subjected to hypoxic stress (3.0 ± 0.2 mg/L and 1.2 ± 0.2 mg/L) for 24 h and 12 h reoxygenation to systemically evaluate indicators of glucose and lipid metabolism. A regulatory network was constructed using RNA-seq to further elucidate the transcriptional regulation of glucose and lipid metabolism. During hypoxia for 4 h, the liver glycogen, glucose and pyruvic acid contents significantly decreased, whereas plasma glucose content and liver lactic acid content increased significantly. The accumulation of liver triglycerides and non-esterified fatty acids was enhanced during hypoxia for 8 h. The activity of key enzymes revealed the different metabolic responses to hypoxia exposure for 4 h, including the enhancement of glycolysis, and inhibition of gluconeogenesis. Furthermore, hypoxia exposure for 8 h increased lipid mobilization, and inhibited the ß-oxidation. In addition, an integrated regulatory network of 9 major pathways involved in the response to hypoxia exposure was constructed, including HIF signaling pathway, VEGF signaling pathway, AMPK signaling pathway, insulin signaling pathway and PPAR signaling pathway; glycolysis/gluconeogenesis, pyruvate metabolism, fatty acid degradation and fatty acid biosynthesis. Additionally, reoxygenation inhibited glycolysis, and promoted gluconeogenesis and lipid oxidation, but energy deficits persisted. In short, although the mobilization and activation of fatty acid in liver were enhanced in the early stage of hypoxia, glycolysis was the main energy source under acute hypoxia. The extent and duration of hypoxia determine the degree of change in energy metabolism.

Effects of dietary supplementation of golden apple snail (Pomacea canaliculata) egg on survival, pigmentation and antioxidant activity of Blood parrot.

This study aims to evaluate the effects of supplementing golden apple snail (Pomacea canaliculata) eggs powder (EP) in the diet as a source of natural carotenoids on survival, pigmentation and antioxidant activity of Blood parrot. A total of 90 fish were divided into three treatment groups with three replicates per treatment. Blood parrot were fed with diets containing 0 (control), 5 % (EP 5 %), and 15 % (EP 15 %) dry powder of golden apple snail egg for 60 days, and nine fish per group were sampled at 20, 40, and 60 days. No differences in survival of the fish among treatments were found throughout the experiment. The body coloration of Blood parrot was enhanced in the skin and caudal fin with increasing content of golden apple snail egg powder in the diet. At the end of the experiment, the carotenoid content in the caudal fin and the number of scale chromatophores of the fish fed dietary with EP were higher (P < 0.05) than those of the control group. The EP 15 % treated fishes showed a significant higher (P < 0.05) in the activities of SOD after 60 days, but we could not observe significant changes (P > 0.05) in CAT activities. Results demonstrated that golden apple snail eggs can be used as a colorant to promote the pigmentation efficacy of Blood parrot.

Erratum to: Effects of dietary supplementation of golden apple snail (Pomacea canaliculata) egg on survival, pigmentation and antioxidant activity of Blood parrot.

[This corrects the article DOI: 10.1186/s40064-016-3051-2.].