Effects and molecular regulation mechanisms of saline-alkali stress on the healthy grass carp

Purpose:Salinity is an important environmental factor that affects the physiological activities of fish. The goals of this study are investigating the effect of different saline-alkali stress on grass carp (Ctenopharyngodon idella). Methods: Grass carp individuals, averaging 12 cm in body length, were obtained from Duofu fish farm (Wuhan, China) and cultured at recirculating aquaculture system for 2 weeks before the experiment began. For the challenge, all grass carp were randomly divided into three groups, and then cultured at saline-alkali water with the concentration of 0, 3‰ and 6‰. After 30 days, some grass crap cultured at 3‰ and 6‰ saline-alkali water were injured. At the same time, gill samples of grass carp were collected from 0, 3‰ (grass carp was not injured), 3‰ (grass carp was injured), 6‰ (grass carp was not injured) and 6‰ (grass carp was injured)saline-alkali groups. Total RNA of all samples was isolated using TRIzol® Reagent (Invitrogen) according to the manufacturer's introduction. RNA integrity was assessed using an Agilent 2100 bioanalyzer (Agilent, USA). Samples with RNA integrity numbers (RINs) = 7.5 were subjected to cDNA library construction using TruseqTM RNA sample prep Kit (Illumina). Results:A total of 15 were processed for transcriptome sequencing, generating 94.99Gb Clean Data. At least 5.76Gb clean data were generated for each sample with minimum 91.87% of clean data achieved quality score of Q30. Clean reads of each sample were mapped to specified reference genome. Mapping ratio ranged from 88.59% to 92.84%. The expression of genes was quantified and differentially expressed genes were identified based on their expression.Criteria for differentially expressed genes was set as Fold Change(FC)=1.5 and Pvalue<0.05. Fold change(FC) refers to the ratio of gene expression in two samples. These DEGs were further processed for functional annotation and enrichment analysis. Conclusions: Our study represents Effects and molecular regulation mechanisms of saline-alkali stress on the healthy grass carp by using RNA-seqtechnology. Our results show that saline-alkali stress will impair the immune system of grass carp. Overall design: Total RNA was solated from gills of grass carp cultured at saline-alkali water with the concentration of 0, 3‰ and 6‰ for 30 days