OVARIAN ATRETIC RATES AND SEXUAL MATURITY OF EUROPEAN HORSE MACKEREL,TRACHURUS-TRACHURUS (L), IN THE SARONIKOS GULF (GREECE)

Histological sections of European horse mackerel, Trachurus trachurus (L.) ovaries were used to follow oogenesis and to describe the atretic states. Atretic states were used to examine the reproductive cycle du ring two successive reproductive seasons. During the first season, spa wning lasted from December to May, with peak spawning occurring betwee n the end of March and the beginning of April. The duration of the spa wning season for the average female was estimated to be about 3 months . Atretic state 1 (yolked oocytes where <50% were in alpha(alpha) stag e atresia) was the most common atretic condition during the spawning s eason. Atretic states 2 (yolked oocytes where greater than or equal to 50% were in alpha-stage atresia) and 3 (no yolked oocytes present but beta atresia or later atresia stages) increased near the end of the s eason, and at the end of the season, females in atretic state 3 were p redominant. The mean number of potential and past-spawning stages per female increased throughout the spawning season, indicating an increas e in spawning frequency. During the second season, spawning occurred f rom January to May. High numbers of females in atretic states 2 and 3 were noted during the period considered to be the middle of the season , followed by an increase of females classified in atretic state 0 (yo lked oocytes with no alpha-atresia stage), indicating a species flexib ility to different conditions. The use of traditional macroscopic meth ods, such as gonadosomatic and hepatosomatic indices, revealed a confo rmity with the histological data concerning the identification of the spawning season. Total body lengths at female maturity (ML(50)), estim ated histologically and macroscopically, were found to be 211 and 220 mm, respectively.