Growth of carp (Cyprinus carpio) white axial muscle; hyperplasia and hypertrophy in relation to the myonucleus/sarcoplasm ratio and the occurrence of different subclasses of myogenic cells

In white axial muscle of carp addition of new fibres to the muscle mass (hyperplasia) decreased with increasing length of the fish. This was deducted from the decrease in the amount of small fibres. In carp larger than about 40 cm standard length (s.l.) hyperplasia no longer occurred (small fibres were absent) and muscle growth only occurred by means of hypertrophy (growth of existing fibres). The stage of growth in which many new fibres were added showed a relatively fast increase in trunk weight, as calculated from growth curves. During the stage of fast growth with a high occurrence of hyperplasia, the DNA/protein ratio decreased. The high percentage of postmitotic myosatellite cells isolated from carp of 5 cm s.l. suggests that in hyperplasia a subpopulation of already differentiated myosatellite cells formed in an earlier stage of development is incorporated in new muscle fibres. The increase of the relative importance of hypertrophy appears to be correlated to an increase in the percentage of proliferating myosatellite cells 17 h after isolation in vitro. This suggests that in hyperplasia and in hypertrophy different subpopulations of myosatellite cells are involved.