Diet of the yellowfin snook, Centropomus robalito (Actinopterygii: Perciformes: Centropomidae), in the southwestern Gulf of California

Background. The yellowfin snook, Centropomus robalito Jordan et Gilbert, 1881, is one of the most important species in southwestern Gulf of California fisheries. It is caught in estuarine systems by coastal fishermen and as bycatch on the continental platform, by the industrial shrimp fishery. Dietary analysis are important to understanding the trophic interactions and the position of species within a foodweb and to understand the dynamics of marine communities. In this study, we describe the diet of the yellowfin snook in the southwestern Gulf of California and quantify the effects of sex and size on the species’ diet. Materials and methods. Stomachs of C. robalito were obtained from the shrimp fishery that operates off the southwestern Gulf of California. Percentages by number, weight, and frequency of each food category were determined, and the index of relative importance (%IRI) was calculated to define the main food categories. Diet breadth and diet similarity between sexes and among sizes were also calculated. Results. A total of 401 stomachs were inspected, of which practically all (n = 385; 96%) contained food. According to %IRI, the main prey consumed comprised the shrimp Trachypenaeus pacificus (73%), Xiphopenaeus riveti (10%), and Penaeus spp. (7%). Secondary items included: the stomatopod Squilla mantoidea (4%), Unidentified organic matter (UOM, 3%), and the fish Porichthys sp. (2%). Centropomus robalito is a specialist predator with a low diet Breadth value (Bi = 0.14). While there were no significant differences in diet between the sexes (Analysis of similarities [ANOSIM]; R = 0.014; P = 0.50), there were differences among sizes (ANOSIM, R = 0.361; P = 0.01). Conclusion. Centropomus robalito is a second-order predator that feeds mainly on shrimp, which are abundant throughout its distribution area. The feeding strategy of C. robalito fits the optimal foraging theory. This fish feeds on the most abundant species, obtaining a higher energetic benefit than it would obtain from less available prey, or from more mobile and larger prey that would imply expending more energy in the search, attack, and manipulation of these prey.