The feeding habits of the Lessepsian migrant Siganus luridus in the eastern Mediterranean (Kastellorhizo Isle, Dodecanese, Greece) are examined. The stomach contents of 209 specimens, 131–250 mm total length, collected by bottom trammel nets, April 1985 July 1986, were analysed. Feeding intensity was high, although it significantly declined during the spawning period in summer. Siganus luridus feeds on a diverse assemblage of benthonic algae including 24 genera (seven green, eight brown and nine red algae) contributing 84.4% by weight (green algae 3%, brown 70.3%, red 11 %). Posidonia oceanica, diatoms, hydrozoa and sand were also found in the stomachs examined. On an annual basis, Dictyota sp., Cysloseira sp., Sphacelaria sp., Gelidium sp., Dictyopteris membranacea, Kuckuckia spinosa and Padina pavonica predominated in the diet. Diet overlap, on a weight basis, indicated a similar food spectrum during spring and summer which was different from that in autumn.

The high feeding intensity of S. luridus during the year (except for the spawning period), its nonselective euryphagous nature, its high competitive potential, and its position in the food web of the eastern Mediterranean ecosystem are important characteristics that, along with suitable oceanographic and ecological conditions for the development and survival of young stages, have enabled the successful establishment and build-up of the population of this Lessepsian migrant in its new environment. Possible competitive implications in the eastern Mediterranean ecosystem are also discussed.