Effect of the High Temperature on Growth, Metabolism, and Fatty Acid Profile of the Clam Ruditapes decussatus Culture with and Without Substrate

Rising seawater temperatures associated with climate change are expected to increasingly challenge the sustainability of bivalve aquaculture, particularly in estuarine environments where thermal variability is naturally high. The grooved carpet clam (<i>Ruditapes decussatus</i>), a species of high ecological and economic value in southern Europe, is strongly influenced by weather conditions. This study aimed to investigate the effects of a chronic thermal challenge (21 days at 28 °C) on the growth performance, intermediary metabolism, and fatty acid composition of <i>R. decussatus</i> raised with and without substrate. Clams were acclimated to either control (18 °C) or high-temperature (28 °C) conditions, and biometric, biochemical parameters (glucose, glycogen, lactate, triglycerides, and cholesterol) and fatty acid profiles were analyzed. Our results denote that exposure to elevated temperature significantly reduced total weight, tissue biomass, meat yield, and condition index in both clams reared with and without substrate. Thermal stress induced marked metabolic alterations, characterized by increased lactate accumulation and depletion of triglyceride reserves, indicating a shift toward anaerobic metabolism and enhanced lipid mobilization. However, glycogen and cholesterol levels remained largely unchanged. Fatty acid analysis revealed a strong temperature-driven remodeling of lipid composition, characterized by significant reductions in total lipids and unsaturated fatty acids, which highlighted changes in key fatty acids, such as arachidonic acid (ARA; 20:4n-6) and eicosapentaenoic acid (EPA; 20:5n-3). In contrast, docosahexaenoic acid (DHA; 22:6n-3) levels remained unchanged under high-temperature conditions. Principal component analysis confirmed temperature as the main factor structuring fatty acid profiles, while substrate exerted only minor effects. Overall, these findings demonstrate that sustained exposure to sublethal high temperature profoundly affects growth performance, metabolic balance, and lipid homeostasis in <i>R. decussatus</i>, overriding the possible physiological benefits associated with substrate presence. The results highlight the vulnerability of this species to future warming scenarios and underscore the importance of incorporating thermal stress considerations into sustainable clam aquaculture management strategies in estuarine environments.