FEEDING ECOLOGY OF MEDITERRANEAN RAZORFISH XYRICHTHYS NOVACULA IN THETYRRHENIAN SEA (CENTRAL MEDITERRANEAN SEA)

The stomach contents of 196 razorfish (Xyrichthys novacula), collected in the Tyrrhenian Sea (Ponza Island, Italy) between July and December 1994, were examined in order to assess the diet and to analyse size-r elated dietary variation of the species. The diet of X. novacula showe d a strict relationship with well-sorted fine sand (SFBC) benthic spec ies, mostly Mollusca and Echinodermata, as pointed out by the analysis at the specific level of the stomach contents. Mollusca Pelecipoda, e ssentially Acanthocardium tuberculatum and Echinodermata, with Echinoc ardium cordatum, made up 90% of the volume of prey of X. novacula. Mys idacea and Gastropoda were frequent but volumetrically less important. The study showed that male and female X. novacula were not effectivel y segregated by trophic dimension in the study area. The niche overlap between males and females in prey composition was pronounced, as evid enced by the significantly high values of Schoener's index with larger males that showed a greater tendency towards predation of large prey. The increment in length (L.I.) in males, despite a decrease in the pe rcentage body weight increment (B.W.I.), could represent the result of a male reproductive feature: the lack of sperm competition allows the males much more energy to devote to growth than do that of the female s of this species.