Relative efficacy of dietary administration of 3,5,3 '-triiodothyronine (T-3) to different stages of an Indian major carp, Cirrhina mrigala (Hamilton): Growth and economics

Different stages of an Indian major carp, Cirrhina mrigala (Hamilton), i.e. hatchling, fry and fingerling, were fed diets supplemented with 3,5,3'-tri iodothyronine (T-3) at doses of 0, 1, 5 and 10 mg kg(-1) diet for 60 days, and then reared on a hormone-free diet for 120 days to study the growth per formance of fish during the treatment period (TP) and post-treatment period (PTP). Oral administration of T-3 at all the stages resulted in a signific antly higher specific growth rate (SGR) and better food conversion ratio (F CR) in comparison to the control group (P < 0.05). However, the growth resp onse of C. mrigala towards T-3 administration appeared to be stage-specific . At the end of the experimental period of 180 days (60 days TP + 120 days PTP), the optimum dosage of T3 appeared to be 5.0 mg kg(-1) diet for both h atchlings and fry, and 1.0 mg kg(-1) diet for fingerlings, resulting in 62. 08%, 30.22% and 13.33% higher weights than in the control group, respective ly. The cost of hormone for production of 1 kg of fish was lowest in the ca se of hatchlings (Rs 0.54), followed by fry (Rs 7.00) and fingerlings (Rs 1 6.07). Hence, based on the degree of growth response of the fish towards T- 3 administration in addition to its economics, only incorporation of T-3 in the diet of hatchlings appeared to be economical.