Pharmacokinetics, Safety Assessment and Residue Kinetics of Emamectin Benzoate in Rainbow Trout, <scp> <i>Oncorhynchus mykiss</i> </scp> (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.