Co-variation of gonadosomatic index and parameters of length-weight relationships of Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner, 1868), in the eastern Adriatic Sea

Summary Seasonal changes in length–weight relationships (LWRs), gonadosomatic index (GSI) and condition factor of Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner, 1868), were studied. Ranging from 14.8 to 39.1 cm total length (TL), a total of 1245 specimens (605 males and 640 females) was collected in the eastern Adriatic Sea. Samples were taken at monthly intervals (January–December 2003) using bottom trawls. The b values of LWRs (W = aLb) varied during the year with season and condition. Including specimens collected in all seasons, the b values showed that growth of both males and females was positively allometric, i.e. specimens changed shape as they gained weight. The GSI reached maximum values in June and a minimum in December. The condition factor was constant during the pre‐spawning period, lowest immediately after spawning (September), and highest at the end of the recovery phase (December).