Cold stress after swimming fatigue decreases immunity-related gene expression in the spleen of the Chinese sucker.

For migratory fish, passing through the cold, fast flowing water of a dam causes stress, leading to disease and even death. To determine the immune response to cold stress in a dam-lake after swimming fatigue in Chinese sucker (Myxocyprinus asiaticus), the spleen mRNA expression profiles in response to cold stress (CS) after fatigue stress (FS) were compared with that of the control (SS). We identified 40,952 differentially expressed genes (DEGs) in the spleen for at least one comparison among 211,397 unigenes. We identified 11,869 DEGs (4,968 upregulated and 6,901 downregulated), 17,803 DEGs (10,610 upregulated and 7,193 downregulated), and 30,579 DEGs (20,652 upregulated and 9,927 downregulated) in the SS vs. FS, SS vs. CS, and FS vs. CS comparisons, respectively. Enrichment analysis indicated the involvement of the immune system and infectious diseases, including the toll-like receptor pathway, the complement and coagulation cascade, and the natural killer cell-mediated cytotoxicity pathway. There were 2,991 DEGs (271 upregulated and 2,720 downregulated), and 2,878 DEGs (873 upregulated and 2,005 downregulated) associated with these pathways in the SS vs. FS and SS vs. CS comparisons, respectively. In the cold stress after fatigue group, the expression levels of heat shock protein (HSP) 70 and HSP90 genes were significantly upregulated; however, more immune response genes showed significantly downregulated expression in SS vs. CS compared with that in SS vs. FS, including those encoding tumor necrosis factor, C-C motif chemokines (3, 8, and 13), complement components (C3, C4, C6, and C7), immunoglobulin, and cathepsins. Overall, cold stress combined with swimming fatigue from passing the dam resulted in the downregulation of many immune genes, suggesting that the Chinese sucker might have experienced serious immune suppression.

Replacement of fish oil with soybean oil in diets for juvenile Chinese sucker (Myxocyprinus asiaticus): effects on liver lipid peroxidation and biochemical composition.

This study was designed to evaluate the effect of the replacement of fish oil (FO) by soybean oil (SO) on growth performance, liver lipid peroxidation, and biochemical composition in juvenile Chinese sucker, Myxocyprinus asiaticus. Fish (13.7 ± 0.2 g) in triplicate were fed five experimental diets in which 0% (FO as control), 40% (SO40), 60% (SO60), 80% (SO40), and 100% (SO100) FO were replaced by SO. The body weight gain of fish fed SO40, SO60, or SO80 diet was similar to FO group, but diets that have 100% soybean oil as dietary lipid significantly reduced fish growth (P < 0.05). Although the level of SO resulted in increasing crude lipid content of the liver, the level of SO did not significantly alter the hepatosomatic index (HSI). Indicators of peroxidation, such as vitamin E (VE) and thiobarbituric acid-reactive substance (TBARS) contents, were changed as increasing dietary SO. It was shown that the inclusion of SO in the diets increased VE concentrations, but reduced TBARS in the liver and total cholesterol (T-CHO) in the plasma. Linoleic acid (LA) and linolenic acid (LNA) significantly increased in fish liver fed diets that contained SO, but eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and the ratio n-3/n-6 were significantly reduced by the inclusion of dietary SO (P < 0.05). Our results indicated that the inclusion of SO increased the hepatic VE content and reduced lipid peroxidation in fish. However, diet containing 100% SO as dietary lipid could reduce growth performance. Thus, we recommended that 40-80% SO can be used as dietary lipid to replace FO for juvenile Chinese sucker.

Transcriptome analysis of Chinese sucker (Myxocyprinus asiaticus) head kidney and discovery of key immune-related genes to cold stress after swimming fatigue.

For Chinese sucker (Myxocyprinus asiaticus), passing through a dam with fast flow and cold water are always unavoidable, and this process can cause stress, disease or even death. In this study, comparative transcriptome analysis was conducted to investigate the potential immune mechanism in head kidney of M. asiaticus with swimming fatigue stress and cold stress after fatigue. In general, a total of 181,781 unigenes were generated, and 38,545 differentially expressed genes (DEGs) were identified. In these DEGs, 22,593, 7286 and 8666 DEGs were identified among groups of fatigue vs. cold, control vs. cold, and control vs. fatigue, respectively. Enrichment analysis revealed these DEGs were involved in coagulation cascades and complement, natural killer cell mediated cytotoxicity, antigen processing and presentation, Toll-like receptor signaling pathways, and chemokine signaling pathway. Notably, immune genes including heat shock protein 4a (HSP4a), HSP70 and HSP90α genes were significantly up-regulated in fishes with cold stress after fatigue. Differently, more immune genes in control vs. cold compared with that in control vs. fatigue were significantly down-regulated expression, such as claudin-15-like, Toll-like receptor 13, antimicrobial peptide (hepcidin), immunoglobulin, CXCR4 chemokine receptor, T-cell receptor, complement factor B/C2-A3, and interleukin 8. In this study, the number of DEGs in the head kidney was less than that our previous study in the spleen, which we speculated was more sensitive to changes in water temperature than the head kidney. In summary, lots of immune-related genes in the head kidney were down-regulated under cold stress after fatigue, suggesting that M. asiaticus might have experienced severe immunosuppression in the process of passing through the dam.

Genetic diversity analysis of mitochondrial DNA control region in artificially propagated Chinese sucker Myxocyprinus asiaticus.

The genetic diversity of the three major artificially propagated populations of Chinese sucker, an endangered freshwater fish species, was investigated using the sequences of mitochondrial DNA (mtDNA) control regions. Among the 89 individuals tested, 66 variable sites (7.26%) and 10 haplotypes were detected (Haplotype diversity Hd = 0.805, Nucleotide diversity π = 0.0287). In general, genetic diversity was lower in artificially propagated populations than in wild populations. This reduction in genetic diversity may be due to population bottlenecks, genetic drift and human selection. A stepping-stone pattern of gene flow was detected in the populations studied, showing much higher gene flow between neighbouring populations. To increase the genetic diversity, wild lineages should be introduced, and more lineages should be shared among artificially propagated populations.