V.H. Cruz Escalona & L.A. Abitia Cárdenas

Departamento de Pesquerías y Biología Marina, Centro Interdisciplinario de Ciencias Marinas; Av. Instituto Politécnico Nacional s/n; Col. Playa Palo de Santa Rita. Apdo. Postal 592, La Paz, B.C.S., México, 23000. Tel.: +52 (112) 253 44, (112) 253 66. Fax: +52 (112) 253 22; vescalon@ipn.mx

Recibido 21-VII-2001. Corregido 06-IX-2002. Aceptado 03-III-2003.

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.

Key words: Trachinotus paitensis, Carangidae, diet, San Ignacio Lagoon, Mexico.

Trachinotus paitensis is one of 35 species of the family Carangidae distributed in the Center-Eastern Pacific, from California to Chile (Allen and Robertson 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.

Two samplings were realized (May and August 1992) in San Ignacio Lagoon, B.C.S., Mexico (26°38’-27°00’ N and 113°06’-113° 18’ W). The fish were collected with a gill net 140 m long, 3 m wide, and mesh size of 9 cm. The nets were set at sunset (18:00 hours) and recovered at sunrise (06:00 hours). The organisms were injected into the abdominal cavity with a solution of 10% formaldehyde, neutralized with sodium borate.

Atotal 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.

Eleven food components were identified, however benthic invertebrates dominated the diet. Four dietary items accounted for the 80% of the total diet of T. paitensis. By number, the most important dietary items were Bittium spp. (45.9%), mysis of Penaeus spp. (14.8%), portunid megalops (11.7%), Anachis spp. (9.2%) and amphipods (7.1%). Gastropod remains also were important. The rest of food components had low values (<3%).

The most important prey by weight were, Anachis spp. (36.1%), gastropod remains (30.2%) and portunid megalops (9%). The gastropod remains (60%), the portunid megalops (29%), Anachis spp. (18%) and Bittium spp. predominated in percentages for frequency of occurrence.

Also, according to IRI, the gastropod remains (45.7%), Anachis spp. (17.4%), Bittium spp. (14.2%) and the portunid megalops (11.8%) were the most important food components.

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.

Fueron investigados los hábitos alimenticios de Trachinotus paitensis, en la laguna San Ignacio B.C.S., México. Se observó que T. paitensis es carnívoro, y se alimenta principalmente de invertebrados bénticos (los gastrópodos Anachis spp., Bittium spp., y larvas de crustáceos). En conclusión esta especie es un depredador oportunista que tiene un impacto principalmente sobre las poblaciones de invertebrados epibénticos.

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