The effect of planktivorous fish (juvenile Perca fluviatilis) on the taxonomic diversity of microplastic particles-colonized bacterial community

Abstract Very few studies have investigated the influence of fish on the degradation rate of microplastic particles (MPs). It could be expected that their effect might be not only direct, through digestion and passage through the gut, but also indirect, through the alteration of the density and composition of the bacterial community on the surface of MPs. This study aims to test the short-term effects of fish presence altering the water chemical parameters and the abundance and genetic diversity of the aquatic bacteria colonising MPs, which may contribute to their faster degradation. This was tested in a triplicate experiment, with each replicate lasting 10 days in the presence or absence of spherical MPs, polystyrene (Ps) or polyethylene (Pe) and the presence or absence of a perch. The animal was separated from the MPs with a plankton net. We determined the chemical parameters of the water, the number of bacteria in the water and on the MPs’ surface, the taxonomic diversity of bacteria in the water and those present on the MPs using 16S rRNA gene (16S rDNA) sequencing, and the alterations of the MPs’ surface using a scanning electron microscope. The exposure to fish increased the concentration of ammonium, nitrates, and orthophosphates and the number of bacteria in the water, which in turn resulted in an increase in the abundance of bacteria and the number of taxa at the family level on the MPs’ surface. The positive effect of fish exudates on the abundance of bacteria on MPs’ surface was greater in the case of Pe than in Ps. The observed effects did not affect the MPs’ surface in any of the types of plastic during the experiment, but they may play a significant role in MPs decomposition over a longer than applied time period.