Two growth trials were conducted to assess the potential for incorporation of canola seed meal (CSM) as a partial or complete replacement for fish meal in diets of Nile tilapia, Oreochromis niloticus. Fish meal protein in the control diet was replaced progressively (25, 50, 75 and 100%) by either raw canola seed meal (RCSM) in the first experiment or treated (soaking in 0.1 citric acid followed by heating) canola seed meal (SHCSM) in the second experiment, so that each of RCSM or SHCSM was incorporated in the experimental diets at rates of 9.30, 18.60, 27.90 and 37.20% in the diets 2, 3, 4 and 5 (for each experiment), respectively.
The levels of anti-nutritional factors, trypsin inhibitor, total polypenolic compounds and phytic acid in RCSM were determined to be 0.13%, 0.70% and 5.10%, respectively. Soaking in water for 12 hrs destroyed 23.08, 7.14 and 18.04% of trypsin inhibitor, total polyphenolic compounds and phytic acid while soaking in citric acid (0.1% solution for 12 hrs) destroyed 12.31, 17.00 and 30.00% of these compound presented in RCSM, respectively. Soaking in water followed by heat treatment (100°C for 40 min) reduced 80.00, 69.00 and 63.00% of trypsin inhibitor, total polyphenolic compounds and phytic acid in RCSM while soaking in citric acid solution (0.1%) followed by heat treatment (100°C for 40 min) destroyed 63.85, 81.71 and 72.00 of trypsin inhibitor, total polyphenolic compounds and phytic acid, respectively.
Compared to control fish group, replacing fish meal by RCSM at all replacing levels significantly adversed final body weight (BW), body length (BL), weight gain (WG), specific growth rate (SGR) and the same trend was also observed for feed utilization parameters whereas all replacing levels of fish meal by RCSM significantly adversed feed conversion ratio (FCR), decreased feed intake (FI) and protein efficiency ratio (PER).
Results of the second experiment indicated that, replacing of fish meal by SHCSM up to 50% did not significantly affected all growth parameters (BW, BL, WG and SGR) and all feed utilization parameters (FI and FCR) and PER but the higher replacing levels (75 or 100%) significantly adversed all growth and feed utilization parameters.
From economic view, it was observed that replacing 50% of fish meal by SHCSM in tilapia diets reduced feed costs by 22.47% without significant effect on growth and feed utilization parameters.
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