GROWTH AND MULTIPLICATION OF WHITE SKELETAL-MUSCLE FIBERS IN CARP LARVAE IN RELATION TO SOMATIC GROWTH-RATE

A morphometric analysis of white axial muscle of common carp Cyprinus carpio was undertaken in order to quantify increase in fibre size, fib re nuclei and fibre number in relation to somatic growth rate during e arly life. In fast-growing carp larvae fed zooplankton, length and hei ght of fibres from the central part of dorsolateral muscle increased a t the same rate (0.75) relative to the total length of the larvae duri ng the first 2 weeks of feeding. During this period, the number of nuc lei per fibre increased threefold while the number of nuclei per unit fibre surface remained constant. In fast-growing larvae fed a formulat ed diet, the total cross-sectional area of one epaxial quadrant of whi te muscle and the total area of white fibres increased at almost the s ame rate (3.15; 3.23) relative to larval total length during the first 28 days of exogenous feeding. The total number of white fibres increa sed faster (2.07) relative to the total length of larvae than the mean area of white fibres (1.16). Hyperplasia accounted for 64% of muscle growth in these larvae. The proportion of fibres with a width <10 mu m decreased from 72% at first feeding to 14% 28 days later, while the p roportion of fibres with a width >20 mu m which was 0% at first feedin g increased up to 34% in the same time. The recruitment of new white f ibres seemed to be almost the same in the whole muscle quadrant at fir st feeding and 18 or 28 days later but, 8 days after first feeding, a transient significant recruitment of new fibres wits shown at the apex of the myotome. Comparisons between fast- and slow-growing groups of larvae showed that for a given larval total length: (1) the mean width of central while fibres was higher and the proportion of central fibr es with a width <10 mu m was lower in slow-growing larvae than in fast -growing ones; (2) the total number of white fibres was lower for a hi gher total cross-sectional area of white muscle in slow-growing larvae than in fast-growing ones. These results suggest that, in Cyprinus ca rpio larvae, slow-growing conditions are related to a decreased contri bution of hyperplasia to muscle growth. (C) 1997 The Fisheries Society of the British Isles.