Transcriptome and analysis on the complement and coagulation cascades pathway of large yellow croaker (Larimichthys crocea) to ciliate ectoparasite Cryptocaryon irritans infection

• Analysis at the transcriptome level for cryptocaryoniasis in Larimichthys crocea.
• 30,509 unigenes were assembled, with an average length of 1715 bp.
• Coagulation and fibrinolytic system was activated after non-lethal concentration C. irritans infection.
• Alternative complement pathway plays an important role in the early stages of C. irritans infection.
• High concentration infection can significantly suppress the immunity.

Large yellow croaker (Larimichthys crocea) is one of the most valuable marine fish in southern China. Given to the rapid development of aquaculture industry, the L. crocea was subjected to ciliate ectoparasite Cryptocaryon irritans. It therefore is indispensable and urgent to understand the mechanism of L. crocea host defense against C. irritans infection. In the present study, the extensively analysis at the transcriptome level for Cryptocaryoniasis in L. crocea was carried out. These results showed that 15,826,911, 16,462,921, and 15,625,433 paired-end clean reads were obtained from three cDNA libraries (A: 0 theronts/fish, B: 12,000 theronts/fish, and C: 24,000 theronts/fish) of the L. crocea immune-related tissues by Illumina paired-end sequencing technology. Totally, 30,509 unique transcript fragments (unigenes) were assembled, with an average length of 1715 bp. In B/A, C/A, and C/B pairwise comparison, 972, 900, and 1126 genes showed differential expression respectively. Differently expressed immune-related genes (DEIGs) were scrutinized, in B/A pairwise comparison, 48 genes showed differential expression, including 26 up-regulated genes and 22 down-regulated genes in B; in C/A pairwise comparison, there were 39 DEIGs, including 7 up-regulated genes and 32 down-regulated genes in C; in C/B pairwise comparison, 40 genes showed differential expression, including 11 up-regulated genes and 29 down-regulated genes in C. There were 16 DEIGs enriched KEGG pathways, in which the complement and coagulation cascades pathway was the top most DEIGs enriched pathway (B:A = 42; C:A = 28; C:B = 42). The coagulation and fibrinolytic system was in a highly active state after infected by C. irritans with non-lethal concentration; the alternative complement pathway may play an important role in the early stages of C. irritans infection. These results demonstrated that low-concentration infection can significantly induce the immunological response in fishes, however, when fishes were in fatal conditions, the immunity was suppressed.