153. Salmon are graded a number of times before becoming smolts. This is carried out to prevent aggression and cannibalism by faster growing fish on those smaller than them. If there are large size differentials the larger fish may act aggressively and territorially and prevent the smaller ones from feeding. Smolts may be graded five or six times prior to transfer to sea cages at one year and further grading may be required for those fish which take two years to become smolts.
154. Trout may be graded several times during their lifetime. Fry will usually be graded twice before the fish, as fingerlings, are transferred to growing tanks or raceways. During the first few months, grading in trout is done to prevent cannibalism. Thereafter it is carried out for production reasons.