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A major threat to gibel carp aquaculture is an epizootic disease caused by C. auratus herpesvirus (Ca HV). Therefore, breeding of disease resistant strain is one of significant needs for the industry. Polyploids often show enhanced tolerance to abiotic or biotic stress. However, the effects of WGD are complex and the underlying mechanisms remain elusive. In this study, we first synthesized a group of novel amphitetraploids via crossing the eggs of gynogenetic C. gibelio clone A+ with the trypsin-treated sperm of sexual C. cuvieri and then established three gynogenetic amphitetraploid clones with different transferrin phenotypes. They all showed intermediate resistance to Ca HV in relative to their parents. Subsequently, we uncovered distinct transcriptomic response to Ca HV infection in the one amphitetraploid clone (Ca A4n-I) compared with their parents. Interestingly, the coexpression gene network analysis showed that amphitetraploid Ca A4n-I and their paternal C. cuvieri adopted different anti-viral strategies via up-regulating the expression of positive factors or down-regulating the expression of negative factors in immune response respectively. Moreover, we revealed the complicated changes of expression patterns, including additivity, maternal expression level dominance, paternal expression level dominance, transgressive up-regulation, and transgressive down-regulation, in the amphitetraploid Ca A4n-I. After Ca HV infection, the proportions of maternal expression level dominance and transgressive up-regulation increased and more C. cuvieri -derived homeologous genes altered expression patterns in the amphitetraploid Ca A4n-I. The current study not only produces a candidate strain for C. auratus aquaculture, but also provides a transcriptomic picture how a newly synthetic animal allopolyploid to response to virus infection. • Ca A4n-I with higher resistance to Ca HV relative to maternal Cg -A+ was generated. • Distinct transcriptomic changes in response to Ca HV infection in three fish types. • Ca A4n-I and their paternal C. cuvieri adopted different anti-viral strategies. • Complex expression pattern changes were revealed in Ca A4n-I after Ca HV infection. [ABSTRACT FROM AUTHOR]

Mandarin fish (Siniperca chuatsi) is a valuable freshwater fish species widely cultured in China. Its aquaculture production is challenged by bacterial septicaemia, which is one of the most common bacterial diseases. Antimicrobial peptides (AMPs) play a critical role in the innate immune system of fish, exhibiting defensive and inhibitory effects against a wide range of pathogens. This study aimed to identify the antimicrobial peptide genes in mandarin fish using transcriptomes data obtained from 17 tissue in our laboratory. Through nucleotide sequence alignment and protein structural domain analysis, 15 antimicrobial peptide genes (moronecidin , pleurocidin , lysozyme g , thymosin β 12 , hepcidin , leap 2 , β-defensin , galectin 8 , galectin 9 , apoB , apoD , apoE , apoF , apoM , and nk-lysin) were identified, of which 9 antimicrobial peptide genes were identified for the first time. In addition, 15 AMPs were subjected to sequence characterization and protein structure analysis. After injection with Aeromonas hydrophila , the number of red blood cells, hemoglobin concentration, and platelet counts in mandarin fish showed a decreasing trend, indicating partial hemolysis. The expression change patterns of 15 AMP genes in the intestine after A. hydrophila infection were examined by using qRT-PCR. The results revealed, marked up-regulation (approximately 116.04) of the hepcidin gene, down-regulation of the piscidin family genes expression. Moreover, most AMP genes were responded in the early stages after A. hydrophila challenge. This study provides fundamental information for investigating the role of the different antimicrobial peptide genes in mandarin fish in defense against A. hydrophila infection. • 15 AMP genes were identified from the transcriptomes of Siniperca chuatsi , of which nine genes were firstly identified. • Most AMPs in the intestine of S. chuatsi were responded at the early stage (0–48 h) after challenged by A. hydrophila. • The expression of the hepcidin gene was the highest up-regulated in the intestine following infection with A. hydrophila. • The expression of the piscidin family genes were down-regulated in the intestine during A. hydrophila challenge. [ABSTRACT FROM AUTHOR]