Feeding strategy and ontogenetic changes in diet of gurnards (Teleostea: Scorpaeniformes: Triglidae) from the Adriatic Sea

A multi-specific approach in fish diet studies provides further insight into the complexity of trophic interactions in marine communities. The feeding habits of three gurnard species Aspitrigla cuculus, Chelidonichthys lucerna and Eutrigla gurnardus (Scorpaeniformes, Triglidae) from north-middle Adriatic Sea was studied for evaluate prey-resource partitioning amongst species and within species, comparing juveniles and adults diet for each gurnards. A total of 1.818 specimens (390 A. cuculus, 973 C. lucerna, 455 E. gurnardus) was collected by bottom trawling and they were assigned to size classes (juveniles or adults) on the basis of macroscopic evaluation of the gonads. Stomach content were analyzed. A common preference in Crustacea diet was found in all species and size classes considered. Nevertheless gurnards showed distinct feeding behaviour: C. lucerna and E. gurnardus were generalist-opportunistic predators, showing a varied diet based on epi-benthic, bentho-pelagic and necto-benthic preys belonged to different taxon such as Teleostei and Mollusca while A. cuculus may be considered as a specialist feeder, feeding almost exclusively necto-benthic invertebrates. The Morisita’s index calculated for critical size classes (juveniles and adults) pointed out differences. At inter-specific level, a possible diet competition between A. cuculus and E. gurnardus (C>0.65) was found for all size classes combined, due to Lophogaster typicus (Crustacea, Mysida) prey abundance. At intra-specific level, high diet overlap was found between juveniles and adults of C. cuculus (C=0.98) and between juveniles and adults of E. gurnardus (C>0.84). In contrast, C. lucerna didn’t competed with increasing body size (C<0.20) showing a clearly change from crustaceans to piscivorous in its diet preferences. The possibility that A. cuculus and E. gurnardus may be compete for the same prey resources while C. lucerna show food resource partitioning, was discussed. Better understanding of the ecology of these coexisting predators should lead to improved conservation and improved fisheries management.