Optimizing substrate use for sustainable Ivory shells (Babylonia areolata) farming while shifting from seabed to recirculating aquaculture systems

Under natural conditions, Ivory shells ( Babylonia areolata ) exhibit typical nocturnal behavior, characterized by burrowing into the sand substrate during the day and emerging at night to forage. This study investigated the effects of sand substrate presence or absence on the survival, growth, and metabolism of B. areolata under artificial culturing conditions. In a recirculating aquaculture system, after a 60-day culture period, no significant differences ( P > 0.05) were observed in survival rate, weight-specific growth rate, feed intake, or feed conversion efficiency between the two groups. In contrast, the cohesiveness, chewiness, and resilience of foot muscle were significantly higher ( P < 0.05) in the no-substrate group compared to the substrate group. Behavioral monitoring revealed that the total 24-hour distance moved, accumulative duration of moving, and duration of feeding were significantly lower ( P < 0.05) in no-substrate group compared to the substrate group. However, Cosinor analysis indicated that these behavioral parameters did not exhibit significant ( P > 0.05) diel rhythmicity in either group. LC-MS analysis revealed several differential metabolic biomarkers, including arginine, glyoxylic acid, 2-oxoadipic acid, allose, histamine, threonic acid, stearic acid, and all-trans-4-ketoretinoic acid in both groups. Furthermore, quantitative analysis of 23 amino acids showed that the concentrations of nine amino acids, including aspartic acid, were significantly down-regulated ( P < 0.05) in the no-substrate group. Notably, a significant positive correlation ( P < 0.05) was observed between the chewiness index and the contents of histamine, stearic acid, arginine, and all-trans-4-ketoretinoic acid. Overall, this study reveals the behavioral and physiological adaptation mechanisms of B. areolata in the presence and absence of sand substrates, along with providing the a theoretical foundation for facilitating the transformation of aquaculture models and promoting the development of a sustainable aquaculture industry.