Seasonal changes in the selectivity of 40 mm PE codend were investigated in the Eastern Aegean Sea. Selectivity of the same codend was tested for red mullet (Mathis barbatus), by using the same vessel, Fishing ground, towing speed and duration. Four sets of data were collected in spring (4-18 April 2002), summer (10-25 July 2002), autumn (26 September-2 October 2002) and winter (22-23 January 2003). Data were obtained by using covered codend technique, and analysed by using logistic equation with the maximum likelihood method. Four sets of selection curves were analysed and compared using the model developed by Fryer. To investigate the seasonal changes in the condition of the fish, length and weight data were collected from samples taken to cover the whole length range in the catch. Results show that estimate of L(50) in spring is significantly lower than those for other seasons (P<0.05). There is about 10% difference between the mean L(50) values of the best and the poorest seasons, summer (11.1 cm) and spring (10.1 cm), respectively. The L50 values of autumn (10.8 cm) and winter (11.0 cm) lay between these two. Fish were in their best condition and the water temperature was at its highest point of the annual cycle in autumn.