Feeding Physiology of Crassostrea gasar (Dillwyn, 1817) on Isochrysis galbana and Biofloc Diets

Understanding the feeding physiological mechanisms of determined oyster species is fundamental for adaptation and growth stabilization, aiming for gains in aquaculture production. To assess its potential for Integrated Multi-Trophic Aquaculture (IMTA) with shrimp, we analyzed the feeding physiology of the mangrove oyster Crassostrea gasar. In this study, we determined the feeding physiology of the mangrove oyster Crassostrea gasar, a commercially important species in tropical Brazil, under two diets, live microalgae (ISO—Isochrysis galbana) and biofloc (BFT), which were tested at four concentrations (10, 20, 30, and 40 mg L−1), to establish whether this species can effectively utilize BFT as a food source. Results indicated that ISO diet promoted superior filtration, characterized by a higher proportion of feces (F), suggesting a reduced need for intensive particle selection. Both clearance (CR) and filtration (FR) rates peaked at 30 mg L−1 before declining, suggesting a physiological threshold for this diet. In contrast, the BFT diet elicited higher CR and FR values but triggered excessive pseudofeces (PF) production and low net organic selection efficiency (NOSE). This suggests high particle rejection and limited nutritional assimilation. In conclusion, while C. gasar can process BFT, it is metabolically disadvantageous as a sole food source. For an optimal performance, I. galbana concentrations should be maintained at or below 30 mg L−1.