How are host-parasite interactions affected by veterinary anti-parasitic treatment? An experimental approach

The effects of veterinary anti-parasitic compounds on wild fish species and their parasites are poorly investigated. Bithionol, an antibacterial, anthelmintic, and algaecide, is commonly used in aquaculture to control parasitic infections, particularly acanthocephalan (spiny-headed worm) infestations. This study aims to evaluate the impacts of bithionol exposure on European chub (Squalius cephalus) originating from natural populations, and its naturally occurring acanthocephalans. We assessed fish behavioral responses, alongside physiological markers, in addition with response of their parasites (number, size, reproductive outputs). Our results indicate that bithionol exposure induces behavioral alterations (increased opercular movements, altered spatial positioning), but does not significantly affect key physiological markers. Furthermore, acanthocephalan parasites influence host immunity and behavior, but their presence does not mitigate (decrease or increase) the effects of bithionol on fish. Contrary to expectations, bithionol treatment does not affect parasites, suggesting potential resistance or environmental factors affecting its efficacy.