In the intensive fish farming, use of specific feeds with immunostimulant compounds is rising. Application of immunostimulant agent can reduce the need of antibiotics. Disease prevention is highly important for maintaining healthy offspring. Microalgae contain potential sources of natural immunostimulant agents therefore they can serve as alternative, immunostimulants and protective agents against fish diseases.
In order to investigate their possible use in fish feed, multiple strains of microalgae were isolated from Hungarian freshwater samples. The strains were selected and characterized based on their growth capacity and content of potential immunostimulant agents (like PUFA, carotenoids, beta glucan, etc.) against diseases specific to early-stage fish cultures. Based on our results the isolated alga strain has favorable growth parameters and is rich in the investigated bioactive compounds.
The immunostimulant potential of the algae strains were also tested in vivo in feeding tests using juveniles of rainbow trout (Oncorhynchus mykiss). The feeding experiments with algae were performed in intensive recirculation fish rearing system where different levels of algae inclusion in fish diets were tested. During the in vivo trial the production parameters and nutrient utilization of the feeds were evaluated. There was no significant difference in growth and production parameters of fish in the treated and control groups.
Beside these parameters the following non-specific immunological parameters were tested: lysozyme, total protein and immunoglobulin levels of blood plasma. The alga treatment had a slightly positive effect on the immune status.