Effects of partial replacement of fish oil by beef tallow fat and canola oil on growth and feeding parameters and carcass composition of rainbow trout (Oncorhynchus mykiss)

To investigate the effects of partial replacement of calf fat and canola oil instead of dietary fish oil on the growth performance and chemical composition of rainbow trout, 250 fish with an average weight of 22.2 ± 0.6 g and a density of 20 fish per 500-liter fiberglass tank were distributed and fed over a 90-day period. Experimental treatments (3 replicates each) were as follows: Treatment 1 (control = T1): adding 100% fish oil to the diet; Treatment 2 (T2): replacement of fish oil with 50% canola oil; Treatment 3 (T3): replacement of fish oil with 50% beef tallow fat; Treatment 4 (T4): replacement of fish oil with 25% beef tallow fat and 25% canola oil. According to the results, the highest rate of weight gain, biomass increase, survival rate and the lowest feed conversion ratio were observed in the control and T4. The lowest percentage of weight gain, specific growth rate, daily growth index and feed, protein and fat efficiency ratios were measured in T3. According to the results, the protein production and fat production values were the highest in T3, exhibiting significant differences with other experimental treatments. The results showed that the amount of moisture in T3 was significantly lower than in the other treatments. In addition, the amounts of fat in T3 and T4 were significantly higher than in the control and T2. The lowest percentage of protein was observed in T2. In conclusion, using a combination of animal fats with vegetable oils and fish oil has a much better effect compared to using each of them alone with fish oil. Therefore, treatment 4 (replacement of fish oil with 25% beef tallow fat and 25% canola oil) is recommended in terms of the studied parameters.