The warming of the sea: challenges and solutions for seabream and seabass 

The rise in sea surface temperature impacts directly on the growth and health of economically valuable fish species, such as seabream and seabass, by altering the environmental conditions in the Mediterranean Sea. One third of species in such elevated species can expect to be impacted by up to 5°C over their thermal limit by 2100, with hypoxia and metabolic stress consequences. Skretting's HT02 functional feed is an innovative solution that helps fish better cope with challenging environmental conditions thus reducing heat stress impact and possible mortalities.


 

The Mediterranean Sea as a model

Temperatures in the Mediterranean Sea has increased rapidly, significantly disrupting the equilibrium of marine ecosystems. Since the mid-1980s, the average surface temperature of the Mediterranean has increased by nearly 0.6°C (Allen et al. 2012), with a further increase of 2-5°C predicted by 2100 (IPCC, 2007). This warming modifies the habitat of fish species of economic interest, such as seabream (Sparus aurata) and seabass (Dicentrarchus labrax), cornerstones of Mediterranean aquaculture. Not only do increasing temperatures reduce the solubility of O2 in the water, exacerbating the risk of hypoxia, but they also exert metabolic pressure on the organisms and cause damage to the tissues, induce metabolic disorder, and increased sensitivity to pathogens by varying the expression of heat shock proteins such as HSP70 (Madeira et al., 2013).

Fig.1: Average global sea surface temperatures, 1880-2023. NOAA Extended Reconstructed Sea Surface Temperature, Version 5, February 2024.

Aquaculture: seabass and seabream

Seabream and seabass aquaculture represents a leading species group in Mediterranean aquaculture, producing annually volumes exceeding 400,000 tonnes (FAO, 2023), with a 25% growth over the last decade. This is because they have a high nutritional yield and are used across climates and farming conditions. However, above the critical temperature — defined as, in the case of seabass, 26°C and, for seabream, 28°C — growth rates are significantly lower, feed conversion is poor, and mortality is high.  Moreover, histological studies have demonstrated fish exposed to higher temperatures suffered of severe hepatic, gills, and intestinal lesions (Hernandez et al., 2003), thereby underlining the need for such targeted interventions.

Skretting new functional feed: HTO2

A solution to these challenges comes through functional feeds that improve the resilience of seabream and seabass under heat stress challenges. With this aim in mind, fish feed nutrition frontrunner Skretting has formulated HTO2 functional feed. HTO2 also differentiates itself with its multifactorial approach, promoting the production of red blood cells to maximize tissue oxygenation (Skretting, 2023), enhancing intestinal function via supplements that lower nutrient loss and pathogen susceptibility, as well as amplifying the natural antioxidant system and, therefore, lessening cell injury by free radicals. In field studies, the product has shown a 15% increase in growth rate as well as a 20% decrease in summer mortality (Skretting, 2023).

Fig.2: Skretting HTO2 mode of actions.

Mediterranean aquaculture, along with similar efforts in other basins worldwide —such as the Red Sea— is showing a remarkable capacity for adaptation, but the effects of climate change are demanding an integrated approach. HTO2 is a prime example of how scientific innovation can contribute to the productive and sustainable future of the sector. In a world where demand for fish continues to increase, it is essential to ensure a balance between economic needs and the protection of marine ecosystems. To tackle the major challenges ahead, it is important to adopt solutions based in technological innovation and promote synergetic collaboration between industry, research, and public institutions.  

Bibliography:

  1. Allen, S.K., Barros, V., Burton, I., et al. (2012). Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. Cambridge University Press, Cambridge, UK.
  2. (2007). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK.
  3. Madeira, D., Vinagre, C., Rosa, R., et al. (2013). "Sea warming affects bream (Sparus aurata) tissues and stress proteins (HSP70)." Microscopy and Microanalysis, 19(Suppl 4), 1-83. doi:10.1017/S1431927613001037.
  4. (2023). The State of World Fisheries and Aquaculture 2022. Food and Agriculture Organization of the United Nations, Rome.
  5. Hernandez, A., Gouveia, S., Nakagami, A., et al. (2003). "Effects of high water temperature on metabolic rates and histological parameters in seabream (Sparus aurata)." Ecological Modelling, 165(1), 13-22.
  6. (2023). HT02 Product Brochure. Skretting Aquaculture Innovation, Mediterranean Division. Accessed from company resources.