Seasonal variation in feeding activity and fatness of cultured oysters in the Merbok Estuary, Malaysia

To identify the optimal harvesting season for oysters cultivated in the Merbok Estuary, located in the northern region of the west coast of the Malay Peninsula, we examined the size and body condition of oysters collected monthly from January to December 2024. The fatness index, calculated as an indicator of oyster condition, increased from January to May and then declined from June to December. Similarly, the concentration of plant pigments in the midgut gland tissue, used as a proxy for feeding activity, exceeded 200 μg/g from January to May, but fell below this threshold in August. These findings suggest that the higher fatness index observed in the first half of the year is attributable to increased feeding activity during that period. Additionally, chlorophyll-a concentrations in the farming waters frequently reached red tide levels from January to May, whereas the dissolved oxygen levels remained favourable. Principal component analysis further supported the conclusion that oysters in the Merbok Estuary exhibited enhanced feeding activity and body condition from January to May. Based on these results, January to May is the optimal season for oyster harvesting in this region.