Black gobies, Gobius niger L., 1758, were sampled monthly between March 2003 and February 2004 in Izmir Bay involving 1149 specimens. Length distribution varied between 5.1 and 15.2 cm total length. Age determined from direct reading on otoliths was comprised from zero to five years. There were significant differences in mean lengths at age group for the two sexes, which did not allow the use of combined data. The parameters of the fitted Von Bertalanffy growth equation (with seasonal component, birth date on the 1st of January) were L∞= 16.69 cm, k= 0.301 yr-1, t0= -2.205 for males, and L∞= 14.84 cm, k= 0.321 yr-1, t0= -1.459 for females. Macroscopic examination of the gonads, and analysis of the monthly values of the gonadosomatic index, indicated that reproduction starts in March and lasts during October, with a maximum in March, followed by August and October. Individuals become sexually mature around 7.80 cm TL (a size that can be reached in less than 1 year) for females. In this population, the sex ratio (male:female) was 3.6:1. Stomach contents were mainly Mollusca (%IRI= 47.53), Crustacea (%IRI= 42.94), Polychaeta (%IRI= 8.26), Foreminifera (%IRI= 1.14) and Teleostei (%IRI= 0.13).
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