Integrated Analysis of Survival, Physiological-Biochemical, and Transcriptomic Changes Reveals the Impact of Saline Stress on the Freshwater Snail .

Salinity is an important abiotic stress that affects metabolic and physiological activities, breeding, development, and growth of mollusks. In this study, we investigated the effects of a range of water salinity on the apple snail , a highly invasive species and an important pest of rice. To examine the molecular response of to salinity, we recorded young snails grown in a saline water environment for 4 months and compared their physiological and biochemical parameters with those of freshwater snails. We used RNA-seq analysis to identify genes and biological processes involved in response to salinity. The results showed that saline water stress reduced the survival rate of the snail population, increased their feeding rate and snail weight, and led to an increase in shell strength and thickness, as well as a significant widening of the overall shell morphology. In female snails, the activities of CAT, SOD, and T-AOC were significantly enhanced, while GSH activity, MDA content, and NOS activity showed significant decreases. In male snails, only MDA content exhibited a significant decrease, while ACHE activity showed a significant increase. Based on transcriptome analysis conducted for the liver and gills of the snails, a total of 1,569,678,584 raw reads were obtained from the nine libraries on the Illumina Novaseq 6000 platform. After preprocessing and the removal of low-quality sequences, 1,560,932,792 clean reads were generated. The number of upregulated and downregulated differentially expressed genes (DEGs) in male snails after the saline stress was higher than that in female snails. The DEGs mainly involved oxidative stress, cellular regulation, and response. Saline concentration inhibited the hatching of eggs to a certain extent. Different levels of saline stress significantly affected the contents of free water, bound water, and enzyme activity of their eggs at different hatching stages. These findings provide theoretical support for understanding the saline tolerance of snails.