Two experiments were conducted, in the first experiment six experimental diets were formulated to contain 0 to 50% replacing levels of soybean meal (SBM) in 10% increments and in the second experiment another six experimental diets were formulated to contain 0 to 50% replacing levels of yellow corn (YC) by potato by-product meal (PBM) in 10% increments. All experimental diets of the two experiments were isonitrogenous (30% CP) and isocaloric (3300 ME/kg diet) and P/E ratio of 90 mg protein/kg (ME) and each diet was fed to two replicates of fish groups (20 fish for each replicate).
Results of the first experiment showed that, replacement of SBM by TBM up to 30% significantly improved final fish body weight (BW). Increasing the replacing levels of SBM by TBM up to 50% improved weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER). Results of carcass traits indicated that fish group fed diets TBM10 gained the higher values of dress-out and flesh and the lower percentage of by-products, while the replacement of 50% of SBM by TBM released the lower percentage of dress-out and flesh and the higher percentage of by-products of common carp compared with the control group. Replacing of SBM by TBM up to 40% insignificantly increased the moisture percentage of carp bodies, while the higher replacing level (50%) significantly increased the moisture and significantly decreased the fat content of carp bodies. Fish fed the TBM10 diet gained the higher protein content and the lower ash content of carp bodies, where, fish fed diet TBM50 gained the lower protein content and the higher ash content.
Results of the second experiment showed that the higher replacing level (50%) of YC by PBM in carp diets significantly improved FCR and PER. Incorporation of PBM in carp diets as a replacement of YC at the high levels (40 or 50%) significantly decreased the percentage of dress-out and flesh. Also, increasing the inclusion level of PBM in carp diets significantly increased by-products percentage of carp carcasses. Increasing the replacing levels of YC by PBM in carp at the highest replacing level (50%) significantly decreased the protein content of fish body and the opposite trend was observed for ash content. Compared to the control group, all replacing levels of YC by PBM significantly decreased fat content of fish body.
Replacing 50% of SBM by TBM in carp diets reduces feed costs by 10.93% while replacing 50% of YC by PBM reduced feed costs by 9.41%
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