MUSCLE GROWTH IN THE ANTARCTIC TELEOST, NOTOTHENIA-NEGLECTA (NYBELIN)

A histochemical and electron microscopy study was carried out on muscle growth in demersal stages of the Antarctic teleost Notothenia neglecta Nybelin. The total number of myotomal muscle fibres was similar in fish ranging in body mass from 11.9g to 889g. Post-anal myotomes contained around 17,000 slow muscle fibres and 70,000 fast muscle fibres. Myosatellite cells were extremely rare. The diameter of fast fibres varied from < 10-mu-m to 130-mu-m in the smallest, and from > 40-mu-m to 450-mu-m in the largest fish studied. Slow muscle fibre diameters in the largest fish ranged from > 30-mu-m to 260-mu-m. Even the largest diameter slow fibres contained significant numbers of mitochondria, which suggests that the diffusion of oxygen does not limit metabolism. The results confirm that muscle fibre hyperplasia ceases prior to the demersal stages of the life history, and that subsequent muscle growth is entirely via the hypertrophy of existing fibres. Comparative studies suggest that this may be one of the factors contributing to the relatively slow rate of somatic growth in this species.