Salicornia ramosissima BIOACTIVES AS A FUNCTIONAL INGREDIENT FOR DISEASE RESISTANCE IN EUROPEAN SEABASS Dicentrarchus labrax
Introduction
Salicornia ramosissima is an edible, highly salttolerant halophyte species that has gained attention due to its diverse bioactive compounds, particularly polyphenols (phenolic acids, hydroxycinnamic acids and flavonoids), which are associated with antioxidant, antiinflammatory, and antimicrobial activities (Silva et al., 2021; Nájar et al., 2023; Hulkko et al., 2023). Evidence for its use in fish and shrimp health management is emerging but remains limited. Dietary inclusion of S. ramosissima biomass in Penaeus vannamei juveniles revealed favourable but transient effects on immune and oxidative status (RamosPinto et al., 2024). The authors also highlighted its potential contribution to circular bioeconomy and environmental sustainability, as the plant can grow in harsh environments without competing with fresh water species (RamosPinto et al., 2024). However, Machado et al. (2025) reported that inclusion of 10% nonfood S. ramosissima fraction did not alter growth or immune status but, improved leucocyte response and upregulation of key immunerelated genes in seabass exposed to an inactivated pathogen. Despite these promising findings, important gaps remain. The effects of purified and unpurified bioactive fractions of S. ramosissima on seabass (Dicentrarchus labrax) performance and resilience are poorly understood. Therefore, the present study explored the potential of S. ramosissima bioactive compounds for health management and disease resistance in European seabass following challenge with Photobacterium damselae subsp. piscicida.
Materials and Methods
Juvenile seabass with an average weight of 23.6 ± 0.7g was randomly distributed into 15 tanks (250 L; 5 treatments with 3 replicates of 40 fish each) in a recirculating aquaculture system at CIIMAR facilities. The fish were acclimated for one week and fed a standard commercial diet. After one week of acclimation, fish were hand-fed during four weeks with a control diet (commercial diet) and four experimental diets based on the control and supplemented with two types of bioactive extracts (XAD and Ext3) at inclusion levels of 0.1% and 0.5% (Ext3_0.1%, XAD_0.1%, Ext3_0.5%, XAD_0.5%). The fish were fed daily at 2% of their body weight. Throughout the feeding period fish were maintained at a temperature of 20 ± 0.5°C, a salinity of 32 g/L, and a 12:12 h light: dark photoperiod. At the end of the feeding trial, blood and gut samples were collected (n = 4 fish per tank; 12 per treatment), as well as following 72h post-infection. Subsequently, 15 fish per tank were challenged with P. damselae subsp. piscicida (6 × 104 CFU mL-1). Mortality was monitored daily for 10 days.
Results and Discussion
After four weeks of feeding, no significant differences in zootechnical parameters (weight gain, feed conversion ratio, specific growth rate, survival) were observed, indicating that inclusion of 0.1% and 0.5% of the extracts did not compromise growth performance. While most haematological parameters (i.e., haemoglobin, haematocrit, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration) remained unaltered at 0 h and 72 h post-infection, white blood cell counts were significantly lower in fish fed the Ext3_0.1% diet compared to the control group at 0 h, which also translated in decreased circulating monocytes, lymphocytes and thrombocytes, suggesting an antiinflammatory profile after the feeding period. Following infection, plasma bactericidal activity increased significantly from 0 h to 72 h in fish fed the Ext3_0.5%, XAD_0.1%, and XAD_0.5% diets compared to the control group.
Moreover, Kaplan-Meier survival analysis showed significantly higher survival probability in fish fed at Ext3_0.1% and XAD_0.1%, with approximately twice the survival probability of the control group.
In conclusion, dietary inclusion of S. ramosissima bioactives at 0.1% (both Ext3 and XAD) did not affect zoo-technical parameters but significantly increased survival after P. damselae subsp. piscicida challenge. These results highlight the potential of S. ramosissima extracts as functional ingredients for enhancing disease resistance in European seabass aquaculture.
Acknowledgements
This work received funding from UKRI and from the European Union's Horizon Europe research and innovation program (GA No. 101084651 - project IGNITION) and AR was funded by Science and Technology Fellowship Trust, Bangladesh (Memo:39.09.0000. 25.80.2020, date: 21/07/22)
Figure 1: Kaplan–Meier survival curves of European seabass fed experimental diets and challenged with Photobacterium damselae subsp. piscicida (6 × 104 CFU mL-1). Different curves represent the control and extract-supplemented diets.
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