Growth increases produced by bovine growth hormone in grass pickerel, Esox americanus vermiculatus (Le Sueur), and the underlying dynamics of muscle fiber growth

Abstract

The potential for rapid somatic growth and the attainment of large ultimate size in teleosts appears related to the sustained ability to recruit new fibers into the growing axial muscle mass, and the lack of such growth potential to a failure of recruitment which occurs at a relatively small size. However, the muscle fiber growth dynamics in the grass pickerel, a comparatively small, slow-growing esocid, suggested that it possessed the requisite muscle growth characteristics for the attainment of much more rapid growth and larger size than it is normally able to manifest and that such growth potential might perhaps be demonstrated by appropriate hormonal stimulation. Bivine growth hormone (bGH) was accordingly administered by intramuscular injection (40 μg/g every 2 weeks) to two size ranges (“small” and “large”) of grass pickerel (respective initial mean total lengths 14.5 and 20.0 cm), held at 22°C and fed ad libitum on live minnows. Administration of bGH resulted in very marked increases in growth in both “small” and “large” grass pickerel compared to control fish receiving no bGH during the course of a 40-week experimental period. The growth of the bGH-stimulated pickerel was comparable to that of pike and muskellunge (the large congeners of grass pickerel) under field conditions. Thirteen of the bGH-treated pickerel exceeded the Canadian record length of 32.8 cm, and three exceeded the North American record length of 38.1 cm. These results suggest that certain relatively small species (e.g., those whose congeners grow fast and reach larger size) may possess unexpected latent potential for great and sustained enhancement of normal maximal growth and that evaluation of muscle fiber growth dynamics may provide a simple means for detecting species that can be made to display such growth.