Transcriptome Profiling Analysis Reveals Changes in the Antioxidant Defense System, Morphology, and Gene Expression in the Gills of Macrobrachium nipponense Caused by Alkalinity Exposure

The median lethal concentration value of alkalinity tolerance for <i>Macrobrachium nipponense</i> over 96 h is only 14.42 mmol/L with a safety value of 4.71 mmol/L, which is insufficient to perform the aquaculture program in a water environment with high alkalinity. Thus, the present study aims to explore the effects of alkalinity exposure on the gills of <i>M. nipponense</i> through identifying the changes in antioxidant enzymes, morphology, and gene expressions after 1 day, 4 days, and 7 days of exposure under an alkalinity of 10 mmol/L. The activities of MDA, GSH-PX, CAT, T-AOC, and Ca²⁺Mg²⁺-ATPase are significantly stimulated by 62.6%, 6.57%, 32.1%, 33.3%, and 14.9%, compared to those from Day 0 (control group), indicating that these antioxidant enzymes play essential roles in the protection of prawns from the damage of reactive oxygen species caused by alkalinity exposure. In addition, alkalinity exposure results in an increase in the hemolymph vessels, affecting the normal respiratory function of the gills. Transcriptome profiling analysis reveals that short-term alkali exposure (4 days) does not result in significant changes in gene expression in the present study. Furthermore, metabolic pathways, biosynthesis of amino acids, amino sugar and nucleotide sugar metabolism, lysosomes, glycolysis/gluconeogenesis, and phagosomes represent the main enriched metabolic pathways of differentially expressed genes (DEGs) between Day 4 and Day 7. Biosynthesis of amino acids, lysosomes, and phagosomes are immune-related metabolic pathways, while amino sugar and nucleotide sugar metabolism and glycolysis/gluconeogenesis are energy metabolism-related metabolic pathways, indicating that the processes of immune response and energy metabolism play essential roles in the response to alkalinity exposure in <i>M. nipponense</i>. Thus, the DEGs from these metabolic pathways are considered as candidate genes involved in the regulation of alkaline acclimation in <i>M. nipponense</i>. The present study provides valuable evidence for analysis of the adaptive mechanism when exposed to alkalinity, contributing to the survival rate and aquaculture of this species under water environments with high alkalinity.