The nuclear DNA content (2C value) was determined in the commercial fish Galaxias maculatus (Galaxiidae) was determined by microdensitometry of erythrocyte nuclei after Feulgen staining; rainbow trout erythrocytes with a known 2C value were used as a standard. The 2C value of G. maculatus was 2.21 +/- 0.12 pg and its C value was equivalent to 1.105 pg (1,082.9 Mbp). This C value is within the range recorded for other osmeriform species (0.62-3.2 pg). The average sperm head diameter of G. maculatus is lower than the average sperm head diameter of rainbow trout (used as a standard), which coincides with the differences observed in the nuclear DNA content of both species. This information increases the genome data available for G. maculatus and might be useful in future programs dealing with its genetic manipulation.