Pharmacokinetics, Safety Assessment and Residue Kinetics of Emamectin Benzoate in Rainbow Trout, Oncorhynchus mykiss (Walbaum, 1792)

Emamectin benzoate (EB) is widely used in aquaculture to control ectoparasites. The study evaluated the pharmacokinetics, biosafety, and muscle residue depletion of EB. In pharmacokinetics, following administration of a single oral dose of 50 μg/kg EB, plasma and tissues (liver, kidney, gill, intestine, and muscle) were sampled up to 128 h and analysed using LC–MS/MS. EB showed tissue‐specific distribution, with the highest C max (565 μg/kg) and AUC (35,927.69 μg·h/kg) in kidney, and lowest C max (13.07 μg/kg) and AUC (368.40 μg·h/kg) in muscle. The intestine exhibited the longest half‐life (648.33 h), indicating prolonged retention. Biosafety was assessed at 1× (50 μg/kg), 5× (250 μg/kg), and 10× (500 μg/kg) doses for 21 days. Fish tolerated the therapeutic dose (1×) without behavioural abnormalities, while higher doses (5× and 10×) caused dose‐dependent pigmentation, reduced feed intake, and histopathological alterations in major organs. Muscle residues remained below the MRL (100 μg/kg) at the 1× dose. It declined below the MRL by day 21 in the 5× group, and reached below the MRL only by day 14 post‐dosing in the 10× group. These findings support the safe use of EB at recommended levels in rainbow trout, while higher doses increase toxicity and residue persistence.