Impact of toxic cyanobacterial blooms on Eurasian perch (Perca fluviatilis): experimental study and in situ observations in a peri-alpine lake.

Due to the importance of young-of-the-year (YOY) perch in the peri-alpine regions where they are consumed, the microcystin (MC) contamination of YOY perch was analysed both in field (Lake Bourget, France) and experimentally using force-feeding protocols with pure MCs. In-situ, schools of YOY perch present in the epilimnion of the lake were never found in direct contact with the P. rubescens blooms that were present in the metalimnion. However, MCs were detected in the muscles and liver of the fish and were thus assumed to reach YOY perch through dietary routes, particularly via the consumption of MC-containing Daphnia. Force-feeding experiment demonstrates the existence of MC detoxification/excretion processes and suggests that in situ, YOY perch could partly detoxify and excrete ingested MCs, thereby limiting the potential negative effects on perch populations under bloom conditions. However, because of chronic exposure these processes could not allow for the complete elimination of MCs. In both experimental and in situ studies, no histological change was observed in YOY perch, indicating that MC concentrations that occurred in Lake Bourget in 2009 were too low to cause histological damage prone to induce mortality. However, Deoxyribonucleic acid (DNA) damages were observed for both the high and low experimental MC doses, suggesting that similar effects could occur in situ and potentially result in perch population disturbance during cyanobacterial blooms. Our results indicate the presence of MCs in wild perch, the consumption of this species coming from Lake Bourget is not contested but more analyses are needed to quantify the risk.