Aquaculture plays a pivotal role in ensuring global food security and nutrition. Current applied research in this field focuses on improving culture conditions, husbandry practices, and aquafeeds to enhance fish health, growth performance, and welfare. Within this framework, the identification of functional dietary ingredients has gained increasing attention due to their potential to enhance fish resilience under stressful conditions. This study aimed to assess the effects of natural extracts containing functional compounds on the stress response of gilthead seabream (Sparus aurata) post-larvae using a multidisciplinary approach. A one-week feeding trial was conducted to evaluate the impact of functional diets incorporating grape seed and Ulva extracts on 80DAE Sparus aurata post-larvae. The experimental design included a control diet (CTRL) and six test diets containing low, medium, and high levels of grape seed (NLOW, NMEDIUM, NHIGH) or Ulva (ULOW, UMEDIUM, UHIGH) extracts. At the end of the feeding period, growth performance and molecular biomarkers related to stress and antioxidant response were analysed.
Following the feeding trial, fish were subjected to two stress challenges: air exposure and bacterial infection with Photobacterium damselae subsp. piscicida. Survival was monitored throughout the trial and challenge period. Dietary supplementation with the tested extracts did not significantly alter stress biomarker expression under basal conditions. However, after exposure to acute stress, fish fed the ULOW diet exhibited significantly higher GPX1 and GPX4 expression and enzymatic activity compared to the control group, indicating a potential activation of the antioxidant response. Similarly, NLOW, NMEDIUM, ULOW, and UMEDIUM diets tended to increase SOD and HSP70 expression after stress, although differences were not statistically significant. Notably, mortality one hour post-stress was higher in the control group, suggesting a protective role of the supplemented diets against acute stress. Nonetheless, during the bacterial challenge, larvae fed experimental diets showed higher mortality than controls, suggesting that the protective effect observed under acute stress was not maintained against bacterial infection.
Overall, these findings indicate that incorporating bioactive biomasses and natural extracts into early-stage aquafeeds can enhance antioxidant responses and stress tolerance in Sparus aurata larvae. However, further optimization of inclusion levels is required to balance the benefits of functional ingredients and maintain robustness against disease.
Acknowledgments: This study was funded by Interface Mission, project (operation code 01/C05-i02/2022.P148) and by “Pacto da Bioeconomia Azul” (Project No. C644915664-00000026) within the WP5 Algae Vertical, both co-funded by Next Generation EU European Fund and the Portuguese Recovery and Resilience Plan (PRR), under the scope of the incentive line “Agendas for Business Innovation” through the funding scheme C5 - Capitalization and Business Innovation, and SAUDE&AQUA II (MAR-021.1.3-FEAMPA-00018). The technical assistance of EPPO and S2AQUAcoLAB staff was highly appreciated throughout the study.