Compensatory growth assessment by plasma IGF-I hormone measurement and growth performance in rainbow trout (Oncorhynchus mykiss)

This study aimed to show the difference in compensatory growth (CG) with different starvation and feeding periods replications, depending on the IGF-I hormone level in the blood. There were 4 treatments in 3 replications. Other indexes like food coefficient ratio (FCR), specific growth rate (SGR) and daily food intake were also examined during the experiment. Fish were fed twice a day ad libitum as follows during the 65 days. Treatment A (TA): control treatment, continues feeding. Treatment B (TB): 4 weeks of starvation and 5 weeks of re-feeding. Treatment C (TC): 3 weeks of starvation and 5 weeks of re-feeding. Treatment D (TD): 2 weeks of starvation and 5 weeks of re-feeding. Each tank contained 23 fishes in each unit with an initial mean weight (SD) of 47.19 +/- 0.42 (g). Blood was sampled in IGF-I hormone concentration at the beginning of the experiment, at the end of the starvation period and every 12 days in re-feeding periods. There was no significant difference between the treatments in FCR (P > 0.05). TB and TC had significant difference (P < 0.01) in comparison with other treatments in SGR, but no significant difference was observed among them (P > 0.05). IGF-I concentrations came down in comparison with control treatment at the end of the starvation period (Day 29) (P < 0.001), but no significant difference was observed among the treatments at the end of the re-feeding period (P > 0.05). According to the results, TB and TC showed more indexes of CG in comparison with TA and TD. Still IGF-I cannot show the quality of CG alone and other growth relating physiological elements in different feeding diets and regimes will be evaluated in future studies.