Effect of different concentrations of folic acid and riboflavin on some growth, blood and immune indices of rainbow trout (Oncorhynchus mykiss) fingerling

The present study was designed and performed to evaluate the effects of various concentrations of folic acid and riboflavin on some growth, blood and immune indices of Rainbow trout (Oncorhynchus mykiss) fingerlings. For this purpose, 891 fingerling rainbow trout with the average weight of 6-7 g were distributed in 27 fiberglass tanks with 9 treatments randomly (33 fish in each tank). Rainbow trout fingerlings was fed with normal diet and diet containing various levels of folic acid (0, 6 and 10 mg) and riboflavin (0, 20 and 30 mg). At the end of the 60-day period of breeding, 30 fish from each treatment were selected randomly and blood sampling was performed after measuring the growth factors. The results showed that the highest mean body weight gain, specific growth factor, daily growth factor, white blood cells, red blood cells, hemoglobin and hematocrit were observed in fish fed diets containing 20 mg riboflavin and 10 mg folic acid and showed a significant difference with control group and other treatments (P<0.05). In terms of survival rate, there was no significant difference between treatments. Based on the results, the best formula for feeding rainbow trout fingerlings is a combination of 20 mg riboflavin and 10 mg folic acid per kilogram of dry food. Due to the low consumption of vitamins, the use of this formula is economical in cold water fish breeding farms and has economic justification.