The fish larval stage is a critical step in marine aquaculture, with significant efforts focused on improving survival rates and resilience in recent years. Incorporating bioactive compounds into larval diets has emerged as a promising strategy to enhance survival, resistance to stressors (e.g., transport, handling), and overall performance. Microalgae serve as a valuable source of these bioactive compounds. However, their extraction from microalgal biomass often yields limited amounts, complicating the scaling up for in vivo trials and subsequent use at the industrial level.
Due to the costs involved in microalgal extract production and in vivo testing, S2AQUA developed an in vitro screening system with fish cell cultures and pathogenic bacterial strains, to assess bioactivity more efficiently and streamline decision-making processes. These screenings help to evaluate the bioactive compounds’ effects on cell proliferation, antioxidant capacity, and antimicrobial activity against fish pathogens. In this study, we investigated the bioactivity of several fractions (F1-F10) derived from the microalgae Tetradesmus obliquus, grown using agricultural effluents, on the VSa13 fish cell line proliferation and antioxidant potential. Additionally, we assessed the bactericidal properties of these extracts against Photobacterium damselae subsp. piscicida, a common fish pathogen.
Preliminary results indicate that fractions F4 and F6 from effluent-grown Tetradesmus obliquus significantly enhanced cell proliferation, while fraction F8 demonstrated strong antioxidant potential in cells exposed to H₂O₂-induced oxidative stress.
Additionally, the antimicrobial activity results indicated that the Tetradesmus obliquus extracts presented antimicrobial susceptibility and bactericidal activity in some extracts with one of the extracts (F5) presenting antimicrobial activity at 1000 µg/mL against all the tested pathogenic bacterial strains.
This systematic in vitro approach effectively identified promising microalgal fractions for subsequent in vivo testing as aquaculture feed additives. This supports the advancement of sustainable aquaculture through natural, resource-efficient feed solutions that enhance fish health and growth while reducing environmental impact.
Acknowledgments: REALM - Horizon Europe, project co-funded by the European Union (Grant number 101060991).