This study investigates the catch components of a commercially used demersal trawl cod end in Izmir Bay, and reveals some of the morphological characteristics of nine commercial ¢sh species; red mullet (Mullus barbatus), hake (Merluccius merluccius), whiting (Merlangius merlangus euxinus), poor cod (Trisopterus minutus capelanus), tub gurnard (Trigla lucerna), common pandora (Pagellus erythrinus), axillary sea bream (Pagellus acarne), picarel (Spicara smaris) and annular sea bream (Diplodus annularis) in relation to mesh size and shapes. Furthermore selectivity of 40-mm polyethylene netting cod end for red mullet, hake, common pandora, axillary sea bream, picarel and annular sea bream is presented. The results are discussed in a way to understand the probable e¡ects of ¢sh body shape on mesh selectivity.

Farmed gilthead sea bream, Sparus aurata, frequently escape from the sea cages and interact with wild populations. The impact of these interactions on the wild populations will depend, in part, on di¡erences in performance of the bream. This study compared the swimming performance of the wild and farmed ¢sh in a current channel. The absolute critical swimming speed (U crit ) increased with increasing size while the relative U crit decreased. Even at the same length there were noticeable performance di¡erences between the individuals. The wild sea bream have signi¢cantly higher (Po0.05) absolute U crit performance (0.86 AE 0.01m s À1 ) than the farmed ¢sh (0.79 AE 0.01m s À1 ) and signi¢cantly higher (Po0.05) relative U crit performance (4.52 AE 0.05 BL s À1 ) than the farmed ¢sh (4.21 AE 0.05 BL s À1 ). The present study suggests that cultured sea bream may not have the ability to compete with wild sea bream in native seawaters.

The critical swimming speed (Ucrit, cm s−1) value of normal juvenile sea bass (Dicentrarchus labrax) (64.7±6.33) was significantly higher than that of fish with lordosis (60.3±6.66) (P<0.05). Both normal fish and those with lordosis showed increased endurance with increasing length during exercise at a fixed water velocity of 50 cm s−1. This speed was used to investigate the separation possibility of deformed specimen from the normal developed fish based on their swimming performance, and 28% separation was achieved without losing any normal fish by the end of the 10th minute. To achieve a better separation of the deformities from the normal, first grading of the juveniles and then a swimming endurance test is advised.

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