Dietary Protein Hydrolysate From <i>Calanus finmarchicus</i> Reduces Oxidative Stress and Increases Intestinal Health in European Sea Bass ( <i>Dicentrarchus labrax</i> ) Juveniles

The aquaculture industry is in dire need of novel feed ingredients that can improve the health and welfare of farmed fish and shrimp. Zooplankton are natural and underutilized marine resources with the potential to be part of a nutritional solution. The aim of this study was to determine the health effects for European sea bass juveniles fed diets with a protein hydrolysate from the zooplankton species <i>Calanus finmarchicus</i>, a novel raw material for feed ingredients. Calanus hydrolysate (CH) was benchmarked using fish hydrolysates as controls at inclusion rates of 3%-4%, depending on the protein content for each of the hydrolysates to allow equivalent protein levels in the diets. The initial feeding trial was 84 days, with an additional week to perform an inflammatory challenge with a UV-inactivated bacterium. Fish receiving diets with CH inclusion were associated with lower levels of hepatic protein carbonyls, a lower level of calprotectin and higher levels of mucins compared to the control hydrolysate diets. No statistically significant differences among the diets for the biomarkers related to the inflammatory challenge were observed. The study showed that dietary inclusion of CH has the potential to reduce oxidative stress and increase intestinal health, thus, improving the health of European sea bass juveniles. These health-promoting effects, combined with the sustainable origin of <i>C. finmarchicus</i> highlight the potential of CH as a novel functional ingredient for future aquaculture feeds. Its use could contribute to reduced reliance on traditional fishmeal sources, thereby, supporting more sustainable and resilient aquaculture practices.