Digestibility and Utilization of Canola Meal in Practical-Type Diets for Rainbow Trout (Salmo gairdneri)

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Abstract
The digestibility study indicated that dry matter digestibility of canola meal (CM) was low (56.2–60.4%), probably due to the high fiber content of this product and its relatively high level of complex carbohydrates. Energy and protein digestibility of CM were 72.4 and 83.2%, respectively, and the essential amino acid digestibilities were similar to those of protein in the CM. CM cannot successfully replace either soybean meal or fish meal in practical-type diets for young rainbow trout (Salmo gairdneri) without sacrificing growth. Supplementation with additional arginine, lysine and zinc, or energy to CM-based diets did not overcome the growth depressing effects. CM supplementation to the trout diet affected the thyroid gland of the fish, producing a diffuse, microfollicular hyperplasia that increased in severity with increasing CM supplementation. Young rainbow trout appear to be more sensitive to dietary glucosinolates than chinook salmon (Oncorhynchus tshawytscha), and total glucosinolate levels of 158 μg/g or more are deleterious to these fish. We conclude that CM should not, at this time, be included as a feed ingredient in commercial trout diets for young rainbow trout.

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