General characteristics of the diet of Trachinotus paitensis ( Teleostei : Carangidae ) from San Ignacio Lagoon , Baja California Sur , Mexico

The food habits of Trachinotus paitensis, in San Ignacio Lagoon B.C.S., Mexico, were investigated. We observed that T. paitensis is carnivorous, feeding mainly on benthic invertebrates (the gastropods Anachis spp., Bittium spp., and the crustacean larvae). We concluded that T. paitensis is an opportunist predator that impacts mainly on epibenthic invertebrates.

Trachinotus paitensis is one of 35 species of the family Carangidae distributed in the Center-Eastern Pacific, from California to Chile (Allen andRobertson 1994, Smith 1995).This carangid is a dominant species on the ictiofauna of San Ignacio Lagoon (Cruz-Escalona 1998).
Although this zone is part of one of the largest protected natural areas of Mexico ("El Vizcaino"), few studies have been realized for the knowledge of its ictiofauna (Segura-Zarsoza et al. 1997, de la Cruz-Agüero and Cota-Gómez 1998, Cruz-Escalona et al. 2000a, 2000b).Food habits of T. paitensis have not been studied.
The objective of this study is to describe the food habits of T. paitensis in San Ignacio Lagoon, B.C.S., Mexico.
A total of 82 stomachs were examined and prey items were recorded quantitatively, by number (N), weight in grams (W), frequency of occurrence (FO) (Hyslop 1980), and identified to the minimum possible taxonomic level.The Index of Relative Importance (IRI) of Pinkas et al. (1971) was used to determine the importance of each prey type.
Although we found eleven food components within the trophic spectrum of T. paitensis, only four preys dominates their diet (Anachis spp., Bittium spp., and crustracean larvaes), this dietary items accounted for the 80% of the total diet.Carangids have been divided according to food habits in three groups: carnivorous, represented by the genera Caranx and Seriola; plancktophagos, such as Decapterus and Selar; and mollusk consumers, such as the species of the genera Trachinotus.These categories are not absolute, since many species are trophic opportunists and changed their habits during their growth.
There is not other studies about the food habits of T. paitensis, however Finucane (1969) and DeLancey (1989) found that amphipods, pelecypods, and crustaceans (Sphaeroma spp.and Emerita spp.) were the primary prey items in T. carolinus.Monteiro and Rodriguez (1990) and Daneman (1993) also indicated that polychaetes are important in the diet of other carangids.
Ontogenetic changes in food habits of carangids have been reported by Modde and Ross (1983); also DeLancey (1989) found diurnal feeding differences in Florida pompano.In summary, the differences between our results and those of the other studies suggest that it is impossible to make any generalization about feeding habits of carangids.