INFLUENCE OF FISH SIZE ON PROLIFERATION AND DIFFERENTIATION OF CULTURED MYOSATELLITE CELLS OF WHITE AXIAL MUSCLE OF CARP (CYPRINUS-CARPIO L)

The in vitro proliferation [uptake of 5-bromo-2'-deoxyuridine (BrdU)] and the degree of differentiation (presence of desmin) of myosatellite cells isolated from white axial muscle of carp between 3 cm and 27 cm standard length (SL) were examined 17 h after isolation. The fraction of the myosatellite cells that were both desmin positive and BrdU pos itive never exceeded 2% of the total number of isolated myosatellite c ells, irrespective of the standard length of the donor(s). This indica tes that, for carp, the temporal relationship between replication and desmin expression of myosatellite cells is different from that describ ed for myogenic cells of mammals and birds. The percentage of BrdU pos itive myosatellite cells was significantly correlated with standard le ngth: it increased from 10% for carp of about 5 cm SL to 40-50% for ca rp between 20 cm and 27 cm SL. The percentage of desmin positive myosa tellite cells was about 50-60%; it was not significantly correlated wi th standard length. The percentage of myosatellite cells that were bot h BrdU negative and desmin negative showed a stepwise difference in th is percentage with increasing length. Fish smaller than 10 cm SL, had more of these cells (10-40%), than larger fish (which had 0-12%). So, apparently the composition of the myosatellite cell population changes during growth. The low percentage of proliferating cells, and the rel atively high percentage of differentiated (desmin positive) myosatelli te cells obtained from 3-6 cm large carp, suggests that, in these smal l fish, muscle growth strongly depends on the use of a pool of myogeni c cells that has been formed at an earlier stage of their development.