Comparative Study on the Growth, Proximate, and Amino Acid Profile of Edible Oysters Cultivated in Indoor and Outdoor Conditions

A feeding trial was conducted to assess the impact of a microalgal diet and a natural diet on the growth performance, water quality, nutrition, and survival of the edible oyster, Saccostrea cucullata. Four experimental diets, designated as “Chl” (100% Chlorella vulgaris), “Chaeto” (100% Chaetoceros gracilis), “Chl + Chaeto” (50% C. vulgaris + 50% C. gracilis), and “Outdoor” (natural diet), were used to develop the treatments. The growth performance and survival of oysters were evaluated by measuring initial and final weights and counts, alongside daily water quality monitoring, weekly chemical analysis, and nutritional composition analysis of muscle tissue at the end of the experiment. The treatments fed with microalgae showed significantly better growth performance, higher survival, and improved water quality parameters compared to the outdoor treatment (p < 0.05). Multivariate analysis revealed that salinity, total dissolved solid (TDS), conductivity, and dissolved oxygen (DO) positively influenced oyster growth, while temperature, ammonia, and soluble reactive phosphorous (SRP) showed negative associations. Additionally, protein content (29.1%–30.7%) showed no significant difference among treatments, while lipid (11.1%–18.2%) and carbohydrate (30.6%–36.2%) levels varied significantly (p < 0.05), with the highest values in the “Chl + Chaeto” treatment. Moreover, essential amino acids (EAAs) and non-essential amino acids (NEAAs) varied significantly (p < 0.05), with EAAs higher in monoalgal (“Chl” and “Chaeto”) diet, and NEAAs higher in mixed and outdoor treatments. These findings highlight the potential of microalgal diets, particularly monoalgal formulations, in enhancing the nutritional quality and overall performance of cultured S. cucullata.