A study of the field trial effects of Eltosil® (recombinant bovine somatotropin) on growth performance of rainbow trout (Oncorhynchus mykiss)

The major reason application of growth hormone (GH) in fish was commercial use of rapid growth and more replication fish. Numerous studies demonstrated that recombinant bovine somatotropin increased growth rates in several fish species. However, such studies have not been done yet in Iran. This research was taken in two steps. In the first step of experiments, 1200 rainbow trout larvae (Oncorhynchus mykiss) weighing 0.5±0.05 gram were randomly allotted in two groups including: 1) the control group and 2) Eltosil® group, each in three replicate. These larvae were randomly divided in six 100 liter square troughs with a continuous water flow of 1 liter per minute. In the second step of experiments, 600 rainbow trout fry (Oncorhynchus mykiss) weighing 45±1 grams were randomly allotted in two groups including: 1) the control group and 2) Eltosil® group, each in three replicate. These fry were randomly divided in six 2,000 liter round concrete ponds with a continuous water flow of 5 liter per minute. Through and ponds were supplied with a well water (temp. range: 15 2; O2: 7.2 0.2; pH= 8 0.3). In the first step of experiments, the fish were hand-fed with commercial pellets (Biomar) ten times daily at the beginning of the experiments and reached four times daily during continuous growth. In the second step of experiments, the fish were hand-fed with commercial pellets (Cheeneh) four times daily at the beginning of the experiments and reached two times daily during continuous growth. In this research, the fish received of 200g Eltosil® per 100kg BW. The administration method of Eltosil® -mixed feed to fish was once a week for 4 consecutive weeks at each treatment stage, totally 8 times for 12 weeks (once a week, 4 times in the first step; withdrawal for four weeks in the second step; once a week for 4 times in the third step). The aim of this research was to evaluate the effect of Eltosil® (oral recombinant bovine somatotropin 1%) on growth performance in rainbow trout. Accordingly, to calculate growth factors, fish were weighed weekly and their body lengths were measured every other week. At the end of each rearing period (on days 28, 56, 84) the means of whole body weight (WBW), weight gain (WG), average daily growth (ADG), total length (TL), average daily length (ADL), grams of weight gain per gram of food (G/F) in control and Eltosil® groups were calculated. Also, specific growth rate (SGR), condition factor (CF), food conversion rate (FCR), and the percentage of survival ratio in the control and Eltosil® groups were calculated. Moreover, at the end of the rearing period (on day 84), comparative growth rate (CGR), means of WBW, WG, TL, ADL and FCR in the control and Eltosil® groups were calculated. The results obtained in the first step of this research demonstrated that there were no significant differences between growth factors in the control and the Eltosil® groups (p> 0.05) on days 28; 56; 84 of rearing periods. Also, the results of the second step showed that there were no significant differences between growth factors in the control and Eltosil® groups (p> 0.05) on days 28 and 56 of rearing periods. However, in second step of experiments, there were significant differences between means of growth factors in WBW (p= 0.019), WG (p< 0.05), ADG (p= 0.009), TL (p< 0.001), and ADL (p= 0.04) of the control and Eltosil® groups on day 84 in rainbow weighing 45±1 grams. In the same period, there was greater 11.2% CGR in Eltosil® group than the control group. There was no significant difference between the percentage of survival ratio of the control and Eltosil® groups in any rearing periods (p> 0.05). In this research generally, oral administration of recombinant bovine somatotropin (Eltosil®) for eight weeks increased final WBW, WG, ADG, TL, ADL, and CGR in rainbow trout fry weighing 45±1 grams on day 84. This data showed that oral administration of recombinant bovine somatotropin (Eltosil®) was a suitable way to improve growth performance in rainbow trout fry weighing 45±1 grams; but it was not in rainbow trout fry weighing 0.5±0.05 gram.