Introduction
Bacterial infections remain a major constraint in Mediterranean farming of European sea bass (Dicentrarchus labrax), particularly during warm periods when disease pressure is highest. Pathogens such as Photobacterium damselae subsp. piscicida continue to cause significant mortality despite the use of vaccination and improved management strategies. In line with the sector's transition toward reduced use of antibiotics, functional feeds that support the fish's natural defence mechanisms are increasingly considered as preventive health tools.
Materials and Methods
The efficacy of a functional package composed of additives and microingredients was evaluated through two complementary experiments: a controlled bacterial challenge trial and a large-scale farm validation trial. The challenge trial consisted of a seven-week feeding period followed by a bath challenge with Photobacterium damselae subsp. piscicida under controlled conditions in juvenile sea bass (initial body weigh 21.8 g) at 22°C. The field trial was conducted at a commercial sea bass grow-out site, with over 1.6 million fish (initial body weight 185 g), covering a natural high-risk period for bacterial outbreaks (August-November). Mortality was continuously monitored and relative percent survival (RPS) was calculated to compare fish fed a control diet with those receiving the functional additive package.
Results and Discussion
Under controlled conditions, fish fed the functional diet showed significantly improved survival following bacterial challenge, with mortality reduced by 11.9 % compared to the control group, corresponding to an approximate 32% improvement in RPS. Statistical analysis indicated a strong treatment effect, with a 98% probability of direction and an odds ratio of 1.75 whose uncertainty interval excludes 1.0, indicating a statistically significant association. These survival benefits were consistently confirmed under commercial farming conditions, where the functional diet reduced overall mortality during periods of elevated disease pressure. In the field trial, mortality was reduced by 1.69 %, resulting in a 47% improvement in RPS and a 97% probability of direction with an odds ratio of 1.91, corresponding to a 91% higher risk of mortality in the control group compared with the test group.
Conclusions
The combined evidence from controlled challenge and commercial field trials shows that functional feed additives can significantly reduce bacterial-related mortality in European sea bass. Such nutritional strategies represent a robust and sustainable complement to existing health management practices, supporting fish survival during predictable high-risk periods.
References
Gouife, M., Chen, S., Huang, K., Nawaz, M., Jin, S., Ma, R., Wang, Y., Xue, L., & Xie, J. (2022). Photobacterium damselae subsp. damselae in mariculture. Aquaculture International, 30(3), 1453-1480.