Diet of the finescale triggerfish, Balistes polylepis (Steindachner), in the Gulf of California

Context Establishing the roles that different species play within ecosystems is key to understanding how ecosystems function and determining the feeding relationships among species. Aims This study analysed the stomach contents of finescale triggerfish, Balistes polylepis, at two sites in the southern Gulf of California, in order to describe its diet. Methods The prey-specific index of relative importance (%PSIRIi) was determined, diet width was calculated with Levins’ index and the Costello method, and the trophic position was estimated using the R package dietr. Key results B. polylepis is an omnivorous species with a preference for animal material (TL = 3.1) that feeds on a wide range of prey. It is categorised as a generalist predator (Levins’ index, Bi = 0.99). The most important items in the diet were the colonial ascidian Lissoclinum fragile (%PSIRIi = 13.52) at Las Ánimas, and the Xanthidae family (%PSIRIi = 13.24) at San Juan de la Costa. Implications B. polylepis plays an important role. Because it can exploit a broad variety of resources, it participates in trophic interactions with several other species. It is essential to determine the trophic habits of this species in other areas of its distribution.