The effect of emamectin benzoate on mortality, growth and metabolism of the polychaete Capitella sp.

Emamectin benzoate (EMB) is used as an in-feed antiparasitic agent to mitigate sea lice infestations in salmonid aquaculture, potentially entering the marine environment through uneaten feed pellets and feces. The polychaete Capitella sp. is a prevalent species in the benthic environments beneath salmon farms, being both an efficient fish-feces converter due to their deposit-feeding behavior and as susceptible non-target species to EMB exposure. However, the impact of EMB on this non-target species remains unclear. To assess the potential effects of EMB on Capitella sp., bioassays were conducted exposing these worms to four concentrations of EMB (50, 125, 313 and 781 μg/kg) via feed administration over 28 days. EMB absorption by the worms showed a positive correlation with exposure concentration and duration. Residue levels in the group exposed to 781 μg/kg reached 1200 μg/kg at 14 days, stabilizing thereafter. The relative higher mortality rate and reduced wet weight in EMB treatments were observed at the end, but without significant influence. Increasing EMB concentrations inhibited oxygen consumption rates of the worms, and cellular energy consumption increased in the 313 and 781 μg/kg exposure groups on day 7, while no significant effects were observed in all treatment groups. Our laboratory observations suggest that Capitella sp. could accumulate EMB, and high concentrations of EMB may pose a potential risk to Capitella sp. Further studies using field observations are needed to further examine this issue.