The uptake of plant protection products by fish, leading to the occurrence of residues in fish products, can occur following ingestion of feed containing a pesticide residue. Metabolism studies in ruminants and poultry are required under the current regulations, but due to the increasing proportion of plant-derived materials in the diets of farmed fish, residues in products of fish origin need to be evaluated. The guidance document on the nature of pesticide residues in fish has been applicable since 1 January 2014 for applications for the approval of all active substances and applications for the authorization of all plant protection products. Fish metabolism data quantify total residues and characterize the chemical nature of residues which may occur in the edible tissues of fish exposed to pesticides. These data are required when pesticide use may lead to significant residues (generally considered to be > 0.1 mg/kg of the total diet, dry weight basis, in fish feed) for plant protection products that are fat soluble, i.e. substances with log Pow ≥ 3.