Biochemical responses in Magallana bilineata: Leveraging oxidative stress for management of tropical estuaries.

Oysters, known for their environmental sensitivity, are potential bioindicators of stress in aquatic ecosystems. This study investigates the influence of environmental stressors, including salinity, temperature, and dissolved oxygen, on the enzymatic activities of Glutathione S-transferase (GST) and Catalase (CAT) in the gills and digestive glands of the slipper oyster, Magallana bilineata. Monthly sampling was conducted at Setiu Wetland, Terengganu (Malaysia), during the monsoon. Significant monthly variations were observed in temperature (p < 0.0001) and salinity (p < 0.05), but not for dissolved oxygen. Protein concentrations, CAT, and GST activity in gills and digestive glands showed significant differences (p < 0.05) between months, indicating the effect of environmental changes on the physiology of M. bilineata. Spearman's rank correlation revealed a strong positive correlation between protein concentration and GST activity in gills (ρ = 0.68), and a moderate positive correlation between CAT activity in the digestive gland and salinity (ρ = 0.56). Principal component analysis (PCA) explained 47.6% of the total variance, with the first two components (PC1 and PC2) accounting for 27.8% and 19.8%, respectively. These findings suggest that CAT and GST activities in M. bilineata vary with seasonal environmental conditions and may serve as potential biomarker endpoints for future biomonitoring studies. However, additional validation using reference sites and controlled exposure experiments is required to distinguish natural physiological variation from stress-specific responses.