Bacterial infections caused by Photobacterium damselae subsp. piscicida (PDP) continue to affect European sea bass farming, particularly during warm periods when disease pressure is highest. As the aquaculture industry shifts toward reducing antibiotic use, functional feeds that support natural immune defences are gaining traction as part of sustainable health strategies.
This series of trials evaluated the impact of a funcional package composed of additives and microingredients, on sea bass survival under both laboratory challenge and commercial farm conditions. The additives were tested in two distinct trials:
A 7-week bath-challenge trial using P. damselae at CTAQUA (Spain)
A large-scale on-farm validation at a sea bass grow-out site
Figure 1 Total mortality for each of the treatments evaluated under controlled conditions showing 11.9%-points lower mortalities for the Test diet. Bars indicate mean values with 95% uncertainty intervals
Figure 2. Plot of the contrasts as full distributions when comparing Control over Test under controlled conditions with markings for the mean Odds ratio (1.75), 50% (thick line) and 95% (thin line) uncertainty intervals. The colours denote the relation to the zero effect: green denotes a 98% probability of higher mortality in the Control diet versus Test.
Survival Under Challenge Conditions
Fish fed the functional additive diet showed significantly higher survival when challenged with Photobacterium damselae under controlled conditions. Mortality was reduced by 11.9%-points compared to the control group, equivalent to a 32% improvement in Relative Percent Survival (RPS) (Figure 1). Statistical analysis revealed a strong treatment effect, with a 98% probability of direction (PD) and an odds ratio of 1.75 whose confidence interval excludes 1.0, indicating a statistically significant association. Biologically, this corresponds to 75% higher odds of mortality in the control group, demonstrating a clear protective effect of the treatment (Figure 2).
Mortality Reduction in Field Conditions
When tested under commercial farming conditions, the test diet consistently improved seabass survival during a period of elevated disease pressure.
Overall mortality was 1.69%-points lower in fish fed the functional diet, representing a 47% improvement in RPS (Figure 3). Analysis of the posterior distribution indicated a clear effect of the functional additive, with a 97% probability of direction. The odds ratio was 1.91, corresponding to about a 91% higher risk of mortality in the control group compared with the test group (Figure 4).
Figure 3. Total mortality for each of the treatments evaluated under field conditions showing lower mortalities and 47% better RPS for the Test diet. Bars indicate mean values with 95% uncertainty intervals.
Figure 4. Plot of the contrasts as full distributions when comparing Control over Test under field conditions with markings for the mean Odds ratio (1.91), 50% (thick line) and 95% (thin line) uncertainty intervals. The colours denote the relation to the zero effect: green denotes a 97% probability of higher mortality in the Control diet versus Test.
These trials demonstrate that a this functional packagecan improve survival outcomes in sea bass exposed to Photobacterium under both challenge and real-world farming conditions. The consistent reduction in mortality and high probability of direction indicates a reliably protective effect, supporting its use as a nutritional tool for disease management during high-risk periods.
By reducing pathogen-related losses while supporting antimicrobial reduction strategies, this type of functional additive contributes to a more resilient and welfare-oriented sea bass production system
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