Abstract:
Infectious diseases pose a significant challenge to aquaculture, resulting in significant economic losses. Treatment options for viral infections in particular are limited. The use of chemotherapeutic agents has several drawbacks, including adverse health and environmental effects. Therefore, there is an urgent need for new antiviral or therapeutic agents that are effective, affordable and sustainable. This study proposes the use of plant extracts as sources of antivirals that not only contribute to more sustainable aquaculture practices but also utilise by-products from terrestrial industries such as agriculture for the development of these treatments. This study focuses on RGNNV, the most widespread strain affecting numerous fish species, with European seabass being highly susceptible. RGNNV causes up to 100% mortality in larvae and juveniles and significant losses in adult fish by targeting central nervous tissue, particularly the retina and brain, resulting in extensive vacuolization and neuronal degeneration. Symptoms include erratic swimming, loss of appetite and hyperinflation of the swim bladder. In this study, we evaluated the in vivo antiviral activity and immunomodulatory capacity of five plant extracts encapsulated in chitosan and formulated in the feed. First, we assessed the health status of the individuals fed with the supplemented feeds, for 3, 10 and 28 days. We evaluated parameters such as growth, blood biochemistry, haematology and gene expression in various tissues including anterior kidney, intestine and erythrocytes. Results showed a slight increase in growth parameters in the groups fed with the feed supplemented with the plant extracts in comparison with the control. However, blood biochemistry and haematology profiles results varied depending on the treatment and the days on which it was analysed. In addition, the antiviral capacity of the feeds supplemented with the plant extracts was assessed in vivo by means of a challenge with RGNNV. Results showed that some plant extracts increased the survival of the fish by up to 20%. Regarding immunoglobulin titration, we observed an increment in the production of specific IgMs against RGNNV in the case of some plant extracts.
Acknowledgements:
This study was funded by ThinkInAzul programme, GVA-THINKINAZUL/2021/020, supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.1) and by Generalitat Valenciana.