RESUMO
Culter alburnus (topmouth culter)is an economically valuable freshwater fish. However, its insufficient tolerance to dissolved oxygen (DO) and ammonia nitrogen (AN) hinders its industrialisation. 360 experimental fish (4.87 ± 1.10 g) were placed in breathing chambers (oxygen level was 0.70-6.50 mg/L) or water tanks (control AN, 0 mg/L; low AN, 8 mg/L; high AN, 16 mg/L). This study analysed the effects of DO and AN on C. alburnus at physiological, biochemical, and molecular levels. (1) Physiology level: the floating point, coma critical point, and coma point at 20 °C group were significantly higher than those at 30 °C. The oxygen consumption rate of C. alburnus at 20 °C, 25 °C, and 30 °C was (256.65 ± 25.87), (470.47 ± 83.84), and (520.87 ± 55.40) mg/kg.h. The LC50 of AN after 96 h was 24.13 mg/L, and the safe concentration was 2.41 mg/L. The survival rate in the high AN group was significantly lower than that in the other two groups. (2) Biochemistry level: The change curves of antioxidant enzyme activity in the liver tissue under hypoxic stress reached a maximum at 12 h and then decreased. In addition, the increase and decrease in enzyme activity (except malondialdehyde) in the high AN group was lower than that in the low AN group. (3) Molecular level: the angiotensin-converting enzyme and carboxypeptidase genes were the major differentially expressed genes (DEGs) in hypoxic stress, and the DEGs were mainly enriched in the ABC transporter signal transduction pathway. In addition, the serum/glucocorticoid-regulated kinase, stearoyl-CoA desaturase, and 3-hydroxy-3-methylglutaryl-coenzyme A reductase genes were among the major DEGs under high AN stress. The DEGs were mainly enriched in steroid biosynthesis or glycine, serine, and threonine metabolism transporter signal transduction pathways. In summary, it is necessary to focus on the DO and AN during C. alburnus breeding.
RESUMO
As one of the most important aquatic fish, Micropterus salmoides suffers lethal and epidemic disease caused by rhabdovirus at the juvenile stage. In this study, a new strain of M. salmoides rhabdovirus (MSRV) was isolated from Yuhang, Zhejiang Province, China, and named MSRV-YH01. The virus infected the grass carp ovary (GCO) cell line and displayed virion particles with atypical bullet shape, 300-500 nm in length and 100-200 nm in diameter under transmission electron microscopy. The complete genome sequence of this isolate was determined to include 11 526 nucleotides and to encode five classical structural proteins. The construction of the phylogenetic tree indicated that this new isolate is clustered into the Vesiculovirus genus and most closely related to the Siniperca chuatsi rhabdovirus. To explore the potential for a vaccine against MSRV, a glycoprotein (1-458 amino acid residues) of MSRV-YH01 was successfully amplified and cloned into the plasmid pFastBac1. The high-purity recombinant bacmid-glycoprotein was obtained from DH10Bac through screening and identification. Based on polymerase chain reaction (PCR), western blot, and immunofluorescence assay, recombinant virus, including the MSRV-YH01 glycoprotein gene, was produced by transfection of SF9 cells using the pFastBac1-gE2, and then repeatedly amplified to express the glycoprotein protein. We anticipate that this recombinant bacmid system could be used to challenge the silkworm and develop a corresponding oral vaccine for fish.