Population structure (age and sex composition), growth and reproduction of Pacific mullet (Mugil so-iuy) were determined from specimens collected on the eastern Turkish Black Sea coast during May-August 1995. The species has been introduced to Black Sea recently and the age composition of the newly established population varied between 1 and 6, with age group 4 dominant. Total length and weight values ranged from 225 to 667 mm and 101 to 3260 g, and there were significant differences between sexes in favour of the females (P < 0.05). Similarly, mean condition factors of males (0.91 +/- 0.091) and females (0.94 +/- 0.098) were significantly different (P < 0.05). From the length-age and weight-age data for both sexes combined, the following population parameters were estimated: length-weight relationship, W = 0.0099 L-2.98; L-infinity (cm) = 71.9, W-infinity (g) = 3412.7, K = 0.26 year(-1), t(0) = -1.57 year. The sex ratio was 0.9:1 males to females. Age at first sexual maturity was estimated as 3-4 years for males and 4-5 years for females, and spawning period extends from end of May to beginning of July. Total fecundity ranged from 454,300 to 2,366,574, while mean egg diameter was 0.67 +/- 0.136 mm. The total fecundity was highly correlated with total length and the relationship was F = 2.776 L-3.26 (r = 0.88). It has been concluded that the newly introduced mullet species appears to establish a self-reproducing population, the growth rates seem to be much better and age at first sexual maturity earlier than that of the native mullet species.