Search

To study adaptation of largemouth bass (Micropterus salmoides) to hypoxic stress, we investigated physiological responses and lactate metabolism of the fish under acute hypoxia. The objectives of this study were to (a) observe changes in glucose, glycogen, and lactate content; (b) detect the activity of lactate dehydrogenase (LDH) in serum, brain, heart, and liver tissues; and (c) quantify the dynamic gene expression of AMP activated protein kinase alpha (AMPKα), hypoxia-inducible factor-1 alpha (HIF-1α), monocarboxylate transporter 1 (MCT1), monocarboxylate transporter 4 (MCT4), and lactate dehydrogenase-a (LDHa) following exposure to hypoxia. The fish were subjected to two hypoxia stresses (dissolved oxygen [DO] 1.20 ± 0.2 mg/L and 3.50 ± 0.3 mg/L, respectively) for 24 h. Our results showed that hypoxic stress significantly increased the decomposition of liver glycogen and significantly increased the concentration of blood glucose; however, the muscle glycogen content was not significantly decreased, which indicates that liver glycogen was the main energy source under acute hypoxia. Moreover, hypoxia led to accumulation of a large amount of lactic acid in tissues, possibly due to the activity of lactic acid dehydrogenase, but this process was delayed in the heart and brain relative to the liver. Additionally, hypoxia induced the expression of AMPKα, HIF-1α, MCT1, MCT4, and LDHa, suggesting that glycometabolism had switched from aerobic to anaerobic. Our results contribute to a better understanding of the molecular mechanisms of the response to hypoxia in largemouth bass.

Water temperature affects the survival, growth, immunity, reproduction, and productivity of farmed fish. The temperature beyond suitable range will disrupt the normal physiological activity. Common carp (Cyprinus carpio L.) is a representative eurythermic fish; they are able to sense and respond to changes in water temperature by adjusting their physiology. To investigate the miRNAs in common carp at different temperatures, nine liver small-RNA libraries (5 °C, 17 °C, and 30 °C, each group have three biological repetitions) were constructed and sequenced using high-throughput sequencing. A total of 110 known miRNAs were identified. Twenty-nine known miRNAs were differentially expressed compared with in control group. GO and KEGG analysis indicated that the miRNAs may play important roles in metabolism and environment information processing. Specifically, we considered the insulin-signaling and glycerophospholipid metabolism pathway, and the results show that in 30 °C, miR-301a, miR-203b-5p, and miR-210-3p were upregulated; their target genes which are the mechanistic targets of the rapamycin kinase (mtor) gene and the protein kinase AMP-activated catalytic subunit alpha 1 (prkaa1) gene in the insulin-signaling pathway were downregulated. And miR-9-5p, miR-27d, miR-92b-3p, and miR-155 were upregulated; their target genes, 1-acylglycerol-3-phosphate O-acyltransferase 3 (agpat3), CDP-diacylglycerol-inositol 3-phosphatidyltransferase (cdipt), glycerol-3-phosphate acyltransferase mitochondrial (gpam), and phosphatidylglycerophosphate synthase 1 (pgs1), in glycerophospholipid metabolism pathway were downregulated. But in 5 °C, the situation was opposite. These findings suggest that significant changes occur in energy metabolism and metabolic processes with components of the cell membrane in different temperatures, which significantly advance our understanding of the regulatory mechanisms underlying the physiological change of temperature stress-induced in liver, specifically with regard to miRNAs. These data provide a foundation for further studies of the role of miRNAs in environmental adaptation in fish.