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¹ Istanbul University, Institute of Marine Science and Management, 34116, Vefa, Istanbul, Turkey DOI : 10.4194/1303-2712-v13_3_06 Viewed : 4608 - Downloaded : 3965 In this study the spawning frequency of Trachurus mediterraneus was estimated for the first time in the Mediterranean basin. The presence of the late-migratory nucleus stage oocytes and post ovulatory follicles (POFs) in the same ovaries were observed continuously during the sampling period. The daily percentage of spawning females with ovaries containing: late migratory nucleus (MN) stage, POFs (present up to 12-24h from the spawning event) was calculated as 11.7% and 18.6% respectively. The average percentage of females presenting one of the two different states was 15.3% which indicated that Mediterranean horse mackerel had high spawning rates in the Sea of Marmara. Our results indicated that T. mediterraneus is a multiple spawner and females spawn approximately every 6.6 days, therefore 20 times in the spawning period May-August 2009. Keywords : Spawning frequency, post ovulatory follicles, Mediterranean horse mackerel