The proximate composition and heavy metal content of the mangrove oyster Crassostrea gasar from the Andoni River was investigated. Samples were categorized into three class sizes: small (< 25 mm), medium (25-50 mm), and large (> 50 mm) each with 10 sampling units for each class size. Differences across class size were significant for carbohydrate, lipid, and fiber content with their highest mean values recorded as 58.39 ± 0.21%, 6.70 ± 0.10% and 18.22 ± 0.28% respectively. Size-specific differences were detected only for concentrations of lead and zinc which showed maximum concentrations of 0.53 ± 0.02μg/g and 42.69 ± 1.81μg/g respectively. The proximate composition and heavy metal content recorded were generally higher in large-sized oysters and the variations observed were attributed to obvious differences in their class sizes. The remarkably low moisture content recorded in C. gasar was attributed to higher drying temperatures (105°C). Food quality and uptake of heavy metals in tissues of C. gasar generally varied along size gradients, with peak values in large-sized individuals. However, the levels of heavy metals recorded in soft tissues of C. gasar in this study were generally very low and fall within levels expected in tissues of aquatic biota.
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