The effect of alternative feeding sterategies during replacement of fish oil by poultry waste fat on growth, food conversion and haematological parameters of rainbow trout (Oncorhynchus mykiss)

Due to the limitations of fish oil and its high price, the aquatic feed industry needs to find suitable alternatives to fish oil in the aquaculture industry. So the aim of this study was to investigate the effect of replacement of poultry waste fat instead of dietary fish oil with return to main diet strategy on some growth and blood parameters of rainbow trout (Oncorhynchus mykiss) in order to find a suitable alternative to fish oil. 120 rainbow trout juveniles weighing 50.72±2.13 g were purchased and after the adaptation period, 25 fish in each pond were released in a completely randomized design with 5 treatments and 3 replications. Control treatment: fed with normal diet, treatment 1: fed with diet containing mixture of fish oil and poultry fat (50/50) for one month and with normal diet in the second month, treatment 2: fed with diet containing poultry fat for one month and with the normal diet in the second month, treatment 3: fed a diet containing a mixture of fish oil and poultry fat (50/50), treatment 4: fed a diet containing poultry fat. At the end of the two-month period, growth indices and food conversion ratio were measured. Also, 6 fish from each treatment were randomly sampled and blood parameters were measured according to standard methods. There was no significant difference between different treatments in terms of growth, nutrition and red blood cell counts. The amount of hemoglobin in treatments 1 and 4 was significantly lower than the control group. The amount of hematocrit in treatment 4 was significantly lower than treatment 1. The number of white blood cells in treatment 4 was significantly lower than other groups. The lowest percentage of lymphocytes and the highest percentage of neutrophils were observed in the treatment 4, so that the amount of this parameter was significant in treatment 4 with other groups. Replacing poultry waste fat with fish oil and re-feeding with the normal diet due to the high ability of rainbow trout to digest food and convert food into tissue can reduce production costs. Therefore, all treatments except treatment 4 are recommended.