Comparative evaluation of processed soybean meal (EnzoMealTM) vs. regular soybean meal as a fishmeal replacement in diets of rainbow trout (Oncorhynchus mykiss): Effects on growth performance and growth-related genes

A 12-week feeding trial was conducted to compare low and high inclusions of conventional soybean meal (SBM) or enzyme-treated SBM (Enzo) as fishmeal replacements in the diets of rainbow trout, Oncorhynchus mykiss. Six isonitrogenous (43% crude protein) and isolipidic (19% crude lipid) diets were produced: a control diet (fishmeal-based) and five experimental diets replacing fishmeal by 8% or 16% with SBM (low or high SBM, respectively); 8% or 16% with Enzo (low or high Enzo, respectively); and 16% with SBM + Enzo blended with 50:50 ratio (Enzo + SBM). Triplicate tanks, each containing 40 fish, were hand-fed to apparent satiation. Compared with the control, all groups that consumed SBM or Enzo diets had lower growth performance (P 0.05). Whole-body content of some essential amino acids (e.g. isoleucine, leucine and valine) showed a significant corresponding decrease with high dietary SBM inclusions. Trypsin activity in the proximal intestine decreased significantly with increasing dietary SBM and Enzo levels. Hepatic expression of GHR1 was greater in high SBM and high Enzo + SBM treatments compared to the control diet, which exhibited the highest expression of IGF-II (P