Acute alkalinity stress induces functional damage and alters immune metabolic pathways in the gill tissue of spotted scat (Scatophagus argus)

The spotted scat ( Scatophagus argus ), known for its robust osmoregulatory abilities as a euryhaline fish, represents a promising candidate for large-scale aquaculture in saline-alkaline waters. In this study, spotted scat were exposed to control conditions and a treatment group with alkalinity at 30 mmol/L for varying durations (0 h, 12 h, 24 h, 48 h, 72 h, and 96 h). Histopathological analysis, biochemical assays, and transcriptomic evaluation were employed to examine the impact of alkalinity stress on gill tissue. The results indicated that gill tissues exhibited varying degrees of damage when compared to the control group across different time points. Prolonged alkalinity stress resulted in an increased number of chlorine-secreting cells and caused the gill lamellae to curve, display inconsistent orientation, and swell at the base. Biochemical analyses revealed that acute alkalinity stress disrupted oxidative balance, leading to decreased activities of superoxide dismutase (SOD) and catalase (CAT), with a notable minimum observed at 96 h. In contrast, the activities of glutathione peroxidase (GSH-Px), acid phosphatase (ACP), alkaline phosphatase (ALP), and malondialdehyde (MDA) concentration gradually increased with extended alkaline exposure. Transcriptomic analysis of gill tissues from the control and 24 h acute alkalinity stress groups revealed significant changes in gene expression, identifying 513 differentially expressed genes (DEGs), with 292 up-regulated and 221 down-regulated. These DEGs were significantly enriched in pathways related to drug metabolism-cytochrome P450 and drug metabolism-other enzymes. Additionally, pathways involved in arachidonic acid metabolism, as well as arginine and proline metabolism, were found to play critical roles in adapting to alkalinity stress. This study contributes to a valuable insight into the molecular mechanisms underlying alkali resistance in spotted scat.