Diet composition of Euthynnus lineatus and Auxis sp. larvae (Pisces : Scombridae) in the Gulf of California

We compared the diet composition of Euthynnus lineatus and Auxis sp. larvae (August 1984, 1986, and September 1987), two co-occurring fish species in the Gulf of California during the summer. The surface temperature at stations that showed the presence of E. lineatus and Auxis sp. larvae ranged from 28° to 32°C. Diet of E. lineatus larvae was dominated by Oikopleura dioica and copepod nauplii (e.g., Paracalanus sp. and Acartia sp.) and to a lesser extent, fish larvae (e.g., Myctophidae, Clupeidae) among other micro Crustacea. In contrast, copepod nauplii and metanauplii were the dominant prey of Auxis sp. larvae during their larval development. As larvae of both species grew, the variety of prey items consumed increased, with strong diversification in larvae >5 mm of standard length. Similarity in diet composition decreased as larvae grew, from 75% in small larvae to 13% in larger larvae. Prey consumed by E. lineatus larvae were larger than prey of Auxis sp. larvae (ANCOVA, P<0.001). Results showed that these two co-occurring species tended to consume different prey items during the planktonic phase.