Length-weight relationships, gonadosomatic index and condition of Mediterranean horse mackerel, (Trachurus mediterraneus) and horse mackerel (Trachurus trachurus) in the eastern Adriatic Sea

Changes in length-weight relationships (LWRs), gonadosomatic index (GSI) and condition factor of Trachurus trachurus and Trachurus mediterraneus were studied in respect to seasons and fish age. A total of 1245 specimens of T. mediterraneus (ranging from 14.8 to 39.1 cm TL) and 1030 specimens of T. trachurus (ranging from 15.7 to 37.0 cm TL) were collected in the eastern Adriatic Sea. Samples were taken at monthly intervals (January-December 2003) using bottom-trawls. In both species the b values of length-weight relationships (W = aLb) varied during the year with season and condition. Including specimens collected in all seasons, the b values showed that growth of T. mediterraneus was positively allometric ; growth of T. trachurus was isometric. The GSI of T. mediterraneus reached maximum values in June and minimum in December. T. Trachurus showed maximum of GSI in March and minimum in September. The condition factor of both species was constant during the prespawning period, lowest immediately after spawning and highest at the end of the recovery phase. Otoliths were taken for age determination. The best condition in both species had samples which age was in accordance from first to second year of life.