Impacts of dietary cyanobacteria on fish

Development of cyanobacterial water bloom became a common issue all over the world. Cyanobacteria are the most important primary producers in aquatic ecosystems but in some abundant species their secondary metabolites called cyanotoxins seem to be harmful for many animal groups especially mammals but also fish. In fishes, adverse effects have been demonstrated in several studies applying cyanotoxins by unnatural injection. However, cyanobacteria and fish coevolved during ages and therefore the question arises whether cyanobacteria might be even used for fish via oral application (fish diet). The use of cyanobacteria for fish diets is varying including applications of pure cyanobacteria biomass as well as incorporation of cyanotoxin containing cyanobacteria biomass into commercial fish diet. The impacts of cyanobacteria in fish diets administered via the oral route revealed contradictory findings ranging from moderate negative to growth promoting impacts and it seems that any bioaccumulation of microcystins can become depurated by rearing fish in clean water for a short period. According to the results obtained from various experiments, cyanobacteria as primary producers might be used as a component of fish diets especially concerning partial replacement of fish meal. However, the determination of nutrition value and the bioavailibility of nutrients present in cyanobacteria for different fish species needs to be determined. Furthermore thorough research is needed to exclude any harmful problem for the final consumers – humans.