Data analysis A total of 357 fish measuring 16.2-35.9 cm (fl) and weighing 82.2-588.5 g were collected and examined. Each gut was excised, weighed (g) together with its content, and preserved in 5% formalin for 72 hours and then transferred in 70% ethanol. Afterwards, stomach contents were suspended in water in Petri dishes, and all prey were identified to the lowest possible taxonomical level using standard taxonomic keys (Birschetin et al., 1968). Diet composition was considered in terms of weights and numbers of prey organisms. for these purposes the following indices were applied (Hyslop, 1980):