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

## TL;DR

High temperatures harm clam growth and metabolism, altering fatty acid profiles, which could threaten clam aquaculture sustainability.

## Contribution

This study reveals how chronic high temperatures affect clam physiology and lipid composition, emphasizing thermal stress in aquaculture management.

## Key findings

- High temperatures reduced growth, biomass, and meat yield in clams.
- Thermal stress shifted metabolism toward anaerobic pathways and increased lipid mobilization.
- Fatty acid profiles changed significantly, with decreases in ARA and EPA but stable DHA levels.

## Abstract

Increasing seawater temperatures could seriously affect bivalve aquaculture, chiefly in estuarine areas, which are highly sensitive to environmental changes. The grooved carpet clam (Ruditapes decussatus), an ecologically and economically important species in southern Europe, is especially vulnerable to abiotic factors. In this study, clams reared with or without substrate were exposed to elevated (28 °C) and control (18 °C) temperatures for 21 days, and their growth, metabolism, and fatty acid composition were analyzed. High temperature significantly reduced growth, tissue biomass, and meat yield, while inducing metabolic shifts toward anaerobic pathways and increased lipid mobilization. Fatty acid profiles were affected by temperature, observing important variations in total lipids and key unsaturated fatty acids such as arachidonic acid (ARA) and eicosapentaenoic acid (EPA), while docosahexaenoic acid (DHA) remained stable. Sediment presence had only minor effects. These findings indicate that sustained warming could compromise clam health and growth, highlighting the importance of considering thermal stress in the management and sustainability of clam aquaculture.

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 (Ruditapes decussatus), 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 R. decussatus 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 R. decussatus, 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.