Parasitabundansen hos abborre (Perca fluviatilis) längs en trofisk gradient

Sammanfattning

Abstract Eutrophication alters the ecology of lakes and can reshape both fish communities and their parasite communities. As nutrient levels increase, not only primary production increase, but also the conditions governing interactions between hosts and parasites may be altered. My study aimed to increase knowledge of parasites of European perch (Perca fluviatilis) and to examine how their abundance was influenced by eutrophication. I predicted that perch in more nutrient-rich lakes, would harbor more parasites. Moreover, I predicted that large perch would have more parasites. Nine lakes in central Sweden with total phosphorus concentrations ranging from 5 to 62 µg L-1, representing a gradient from nutrient-poor to nutrient-rich conditions, were sampled during autumn 2025. In total 121 perch were examined for the ectoparasitic fish louse (Argulus foliaceus), and 37 individuals within the size range of 28–35 cm were dissected to quantify endoparasites in the gastrointestinal tract. The results showed that the number of fish lice increased by approximately 3.5 % per µg L-1 increase in phosphorus and by 15% per centimeter increase in body length. One endoparasitic species, Camallanus lacustris, was found, but no significant relationship between phosphorus concentration and C. lacustris abundance was observed. The directly transmitted fish louse appeared to benefit from higher nutrient levels, whereas the endoparasite C. lacustris, which has a more complex life cycle, showed only a weak tendency to increase with nutrient enrichment.