Structural changes in freshwater fish and chironomids exposed to bacterial exotoxins

Mass fish mortalities have been reported in the past decade from British waters, often coinciding with blooms of filamentous actinobacteria, particularly strains of Streptomyces griseus. The present study has shown that some fractions of the exudate of S. griseus, prepared after a series of high pressure liquid chromatography (HPLC) separations, and analysed with liquid chromatography mass spectrometry (LC–MS), induced pathological changes to the gills of carp and/or tench fry following exposure under laboratory conditions up to 96h Similar changes were induced by streptomycin, a secondary metabolite of S. griseus, and these included loss of microridging and fusion of secondary lamellae, with carp fry in the case of the exudate of S. griseus being more sensitive than tench fry, especially with exposure to fraction 9 and selected sub-fractions of 9. Some deformities using a severity index were also observed in the head capsule of larvae of the non-biting midge Chironomus riparius, including loss and splitting of teeth on the mentum. The results are discussed in relation to further identification of metabolites derived from samples of the organic filtrate of S. griseus and implications for the functioning of freshwater ecosystems. ► Mass freshwater fish mortalities have increasingly occurred in the UK. ► These events coincide with blooms of filamentous actinobacteria. ► Streptomyces griseus is the most frequently occurring actinobacterium. ► Metabolite fractions of S. griseus cause deformities to fish gills and chironimids. ► Fraction identification allows the development of operational tools for managing events.