NUMBERS OF MUSCLE NUCLEI AND MYOSATELLITE CELL-NUCLEI IN RED AND WHITE AXIAL MUSCLE DURING GROWTH OF THE CARP (CYPRINUS-CARPIO)

We determined the percentages of muscle fibre nuclei and satellite nuc lei over a growth range of carp (Cyprinus carpio), as the increase in the number of muscle fibre nuclei is an important aspect of the increa se in muscle mass, and myosatellite cells are believed to be the sourc e of new muscle fibre nuclei. In white as well as in red axial muscle the percentage of the nuclei present in muscle that are muscle nuclei (muscle fibre nuclei+myosatellite nuclei) remained constant during gro wth (54 and 32% respectively). The difference in the percentage of non -muscle nuclei between white and red axial muscle is mainly caused by the higher content of endothelial nuclei in red axial muscle. In white axial muscle the DNA/protein ratio (nucleus/sarcoplasm ratio) decreas ed between 3 and 15 cm S.L. In red axial muscle we found a continuous decrease in DNA/protein ratio over the entire investigated size range (3-50 cm S.L.). This may be related to a longer occurrence of hyperpla sia in red than in white axial muscle. In both fibre types the percent age of muscle nuclei being myosatellite nuclei decreased with increasi ng length. In white axial muscle it decreased from about 5% in carp of 5 cm S.L. to less than 1% in carp of 20 cm S.L.; for red muscle these values were 11 and 3% respectively. For white axial muscle we calcula ted that, especially in larger fish, the myosatellite cells alone cann ot account for the increase in the number of muscle fibre nuclei durin g growth. The percentage of proliferating nuclei in muscle tissue, mea sured by the uptake of 5-bromo-2'deoxy-uridine, is high enough to acco unt for the total increase in nuclei. So indirect evidence is availabl e that another cell type present in the muscle tissue may also be invo lved in the formation of additional muscle fibre nuclei.