Influence of bovine growth hormone on the growth dynamics of mosaic muscle in relation to somatic growth of rainbow trout, Salmo gairdneri Richardson

Bovine growth hormone (bGH), administered intramuscularly at 20 μg^-1 every 2 weeks, produced faster somatic growth in rainbow trout fingerlings to approximately 30 cm than in those not receiving the hormone. Both groups were maintained at 12° C, with a photoperiod of 16 : 8 LD, and on ad libitum rations daily. The faster growth was characterized by a controlled increase in input of fibres into the mosaic muscle (which dominates the body tissues by its bulk). It is not known if the enhanced input of fibres is an example of the known ability of the mosaic fibre mass to respond with flexibility and precision to widely differing somatic growth rates, or is a specific consequence of the growth hormone. In other fingerling trout receiving 4-5% daily rations and consequently growing slowly, bGH did not stimulate growth or evidently modify fibre input dynamics. Body dry weight, and condition ( K ), though modified by rations and growth rate, evidently had little effect on muscle fibre growth.