A study conducted by the Institute of Aquaculture Torre de la Sal (IATS), a center of the Spanish National Research Council (CSIC), has revealed how extreme heat associated with climate change affects the gut microbiota of gilthead seabream (Sparus aurata), one of the most farmed fish in the Mediterranean Sea. The study proposes feeding strategies to mitigate these impacts and opens new avenues for sustainable aquaculture.

Extreme temperature events in the Mediterranean Sea are becoming more intense and frequent. Monitoring the mechanisms that facilitate the adaptation to the natural environment is becoming increasingly necessary in the context of global change. This is especially relevant in a closed sea like the Mediterranean, with temperature increases significantly higher than those recorded in other latitudes.

Gut microbiota as a biomarker

One of the effects of heat stress is the alteration of the gut microbiota, with the consequences this has on a wide variety of physiological processes, in addition to protecting the host against invasion by foreign organisms. Consequently, the monitoring and regulation of the gut microbiota has a dual objective: its use as a biomarker of heat stress and the effectiveness of corrective measures as a result of genetic selection programs, dietary changes, and/or culture conditions, among other factors.

In this context, during the summer of 2022, coinciding with the record high temperature (30.49°C) on the surface of the waters of the Gulf of Valencia, the IATS-CSIC team evaluated the effect of dietary fat content and the addition of a lipid emulsifier on the microbiota of the intestine and water of gilthead seabream farmed in the center's facilities in Ribera de Cabanes (Castellón). The results showed that heat drastically altered the gut microbiota and increased the presence of the bacterial genus Brevinema, associated with imbalances in gut health.

Adapted feeds

As explained by Fernando Naya-Català, a researcher at IATS-CSIC, "changes in the microbiota are a clear sign of heat stress. However, this effect can be remedied through feeds with reduced lipid levels and the addition of emulsifiers, which can reduce stress markers such as cortisol and blood glucose."

The study included four experimental diets with different combinations of lipid levels (16% and 14%) and the addition of the commercial emulsifier Volamel Aqua, provided by the company Nukamel NV (Belgium). These diets were designed to reduce the physiological stress associated with extreme heat, improve intestinal homeostasis, and restore welfare markers in fish.

"The research focused on measuring how diets affected the composition of the gut microbiota, identifying changes in key bacteria such as Brevinema, a genus that increased significantly under extreme heat conditions. This microorganism is associated with states of intestinal imbalance and was identified as a possible marker of heat stress," said Naya-Català.

In addition, the adapted diets showed positive effects on reducing levels of cortisol and blood glucose, classic indicators of stress in fish. This trial provides valuable information for the design of more climate-resilient feeding strategies and opens up new opportunities to improve the sustainability and efficiency of aquaculture in vulnerable regions such as the Mediterranean.

The research has been carried out within the framework of the European project AQUAEXCEL3.0 and the Next Generation GVA-ThinkInAzul project, with the participation of the Belgian company NUKAMEL NV.

Reference:

R. Domingo-Bretón, S. Cools, F. Moroni, A. Belenguer, J.A. Calduch-Giner, E. Croes, P.G. Holhorea, F. Naya Català, H. Boon, J. Pérez-Sánchez. Intestinal microbiota shifts by dietary intervention during extreme heat summer episodes in farmed gilthead sea bream (Sparus aurata). Aquaculture Reports, Volume 40, 2025, 102566. ISSN 2352-5134. https://doi.org/10.1016/j.aqrep.2024.102566