Acceptability of Rapeseed Proteins in Diets of Rainbow Trout (Salmo gairdneri)

Abstract

Weight gain and feed consumption results showed that rapeseed protein concentrate (RPC) and rapeseed meal (RM) can be substituted for soybean meal (SM) and perhaps partially for herring meal (HM) in rainbow trout (Salmo gairdneri) control (SM–HM) diet and thus have economic benefits. Rapeseed flour (RF) was a poor source of proteins due to its greater effect on thyroid function. Rapeseed proteins have little effect on liver weight, body moisture, liver and body lipid, liver and body sterol content, visual and histological appearance of liver, heart and visceral tissues, or on the flavor, but caused yellow pigmentation of the skin. The levels of individual fatty acids in the diets directly affected the levels of individual fatty acids in the liver and body, while the type and level of dietary rapeseed proteins appeared to have no effect. The levels of fatty acids, 20:1 and 22:1 (includes erucic acid), were lower in the body and even lower in the liver compared with the diets. All test diets, except RPC–HM diet, caused marked thyroid hyperplasia, believed to be due to glucosinolates (goitrogens). However, some compensation for this goitrogenic action must occur because plasma T4 levels indicated a hypothyroid state for only five test diets (highest RPC-containing diet; highest RM-containing diet; all three RF-containing diets). Key words: dietary rapeseed, glucosinolates, feed–gain ratios, growth, lipids, fatty acids, plasma T4, thyroid histology, flavor, weight gain