To assess the number of mitotic divisions in fish spermatogonia, an easy method was devised which can estimate the number of mitotic divisions by only counting the cells in the cross-section of a cyst at its largest diameter. Using clay to simulate spermatogonial cysts, we obtained results which related the number of cells in a cross-section of a cyst at its largest diameter to the total number of cells in the same cyst. The results were then compared to the number of mitotic divisions observed in seven species. The number of divisions estimated from the simulation experiment coincided exactly with the observed values in all species with spherical shaped cysts. However, the counts determined in fish with elliptical shaped cysts differed from the expected values. As a result, it is clear that the obtained values from the simulation experiment are valid for the estimation of the number of mitotic divisions.

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