Effect of extrusion processing on the nutritive value of canola meal for chinook salmon (Oncorhynchus tshawytscha) in seawater

This study was conducted to evaluate three canola protein products as partial replacements of steam-dried whole herring meal (HM) in a practical diet for juvenile chinook salmon in seawater. Groups of 30–40 g chinook salmon held in 9.5–12°C seawater on a natural photoperiod were fed one of seven equivalent protein (390 g kg⁻¹) and isoenergetic (20 MJ gross energy kg⁻¹) diets to satiation. Each of three test protein sources, namely, commercial canola meal (CM), low-temperature extruded CM (90°C; LT), and high-temperature extruded CM (150°C; HT) comprised about 120 and 240 g kg⁻¹ of dietary protein by replacement of 15 and 30%, respectively, of the HM protein in the control diet. Chinook salmon growth and feed intake were markedly depressed by replacing HM protein with a high level of CM, but these responses were not lowered by replacement with LT and HT. The phytic acid content in commercial canola meal was reduced by about 10 and 30% from the original level by extrusion cooking at low (90°C) and high (150°C) temperature, respectively. Therefore, the diets containing HT still had significant amounts of phytic acid. Terminal whole-body zinc contents were inversely related to the dietary levels of the different canola protein products. Thyroid function was altered by CM but this effect was offset by heat treatment. The results suggest that extrusion cooking of CM improves its nutritive value for chinook salmon in seawater. Indeed, it was found that HT could comprise 240 g kg⁻¹ of the dietary protein without adversely affecting performance.