Food and feeding habits of pearly razorfish, Xyrichtys novacula (Linnaeus, 1758), in the southern Tyrrhenian Sea:: variation by sex and size

We collected pearly razorfish, Xyrichtys novacula (Labridae), from a sandy bottom of Capo d'Orlando (Tyrrhenian Sea) to study their feeding habits. We caught fish by hand-lines and seine nets and identified, counted and weighed food items in their stomachs. We evaluated the importance of the different prey types by calculating the frequency of occurrence, abundance and mass. We used these values to calculate the index of relative importance (IRI) for each taxonomic category and a modified index (MI) which did not incorporate %N into the formula. Gammarideans were dominant food items in terms of %F but showed a very low MI value; the bivalve Acanthocardia tubercolata was the dominant species in terms of %W and MI value. The prey items were mostly benthic organisms belonging to the assemblage of fine, well-sorted sands showing that X. novacula is a benthic feeder. Despite the large number of prey taxa found, few species accounted for most of the prey consumed, indicating specialist feeding, as confirmed by the low value of the Levins' standardised index. We found significant differences in prey distribution among size classes, with the highest prey diversity recorded in 120-140 mm TL size classes. Correspondence analysis showed a trend of increasing predator size classes among prey items, with small prey, such as copepods and amphipods, in the smallest predator size classes and bigger prey in the larger ones. Prey caught by larger predators differed significantly in weight from those taken by smaller specimens. There was a significant positive correlation of fish length with bivalves, decapods and echinoids, and a negative one with copepods, ostracods, caprellids, gammarideans. There were no significant differences between males and females of overlapping sizes. Juveniles are able to exploit only small, vulnerable prey, while adults take few, large prey, thereby avoiding competition with juveniles.