Relation between Physiological Variations and Economic Feasibility in Farmed Mangrove Oysters (Crassostrea gasar) in Subtropical Estuary

Abstract This study evaluates the physiological changes in mangrove oyster Crassostrea gasar in adult individuals cultivated in subtropical estuarine environments. To assess mortality at different salinities, 0 to 35 g L-1 concentrations were used. The same salinities were also employed to evaluate the metabolic rate and ammonia excretion. Furthermore, the oysters were exposed to different temperatures (15, 20, 25, and 30°C) to assess the metabolic rate and ammonia excretion. The mean mortality significantly decreased after a salinity of 4 g L-1. Another objective was to verify, based on the survival conditions found in the different salinities tested, 63% in salinities between 5 and 10 g L-1, 72% for salinity between 11 and 19 g L-1, and 81% for salinities between 20 and 30 g L-1, the economic viability of cultivating the mangrove oyster, practiced in the region, in 0.1 ha. The financial indicators of Gross Revenue and Operating Profit, as well as the profitability indicators of Gross Margin and Profitability Index, showed positive values in all three proposed survival conditions. Due to the particularities described here, in all tested conditions, at the selling price of a dozen oysters of US$ 4.00, there was economic viability with profitability always higher than the minimum attractiveness rate of 10.5%.