Canola Meal in Rainbow Trout (Salmo gairdneri) Production Diets

Abstract

Production diets containing up to 20% canola meal were fed for 108 d to rainbow trout (Salmo gairdneri) to evaluate the effects on weight gain, food conversion, thyroid function, and organoleptic quality of market-sized fish. Weight gain was not affected by dietary canola meal level. Food conversion values and organoleptic properties were not influenced by dietary treatments. Feed costs were reduced by $18.70 (U.S.) per metric ton compared to control diet at the highest level of dietary canola meal (20%). Thyroid function was significantly affected by dietary canola meal. Dose-related changes in the histological appearance of the thyroid and alterations of plasma thyroxine and 3,5,3′-triiodothyronine levels indicated that compensatory adjustments in thyroid function allowed normal growth to proceed in the canola-fed fish. Possible mechanisms of dietary glucosinolate influence on thyroid function are discussed and areas for future research are suggested.Key words: canola meal, plasma T₄, plasma T₃, thyroid histology, goitrogen, glucosinolates, trout growth, food conversion, least-cost diets, organoleptic quality