Stomach contents of two planktivorous fishes of the gulf of california during summer 1991

Se examinaron contenidos estomacales y aparatos filtradores de ejemplares adultos de sardina monterrey (Sardinops caeruleus) y sardina crinuda (Opisthonema libertate), recolectados en el Golfo de California, con el fin de describir su alimentacion. Ambas especies son filtradores omnivoros que presentan un espectro trofico amplio, mostrando indices de selectividad elevados hacia algunos grupos planctonicos, siendo la frecuencia de estos directamente proporcional a su abundancia en el plancton. El traslapo por alimento, tanto en numero como en volumen, fue alto entre las dos especies. Los adultos de ambas especies presentan espacios interbranquiespinales muy reducidos, en comparacion con los individuos de menor tamano, siendo estos de 90.20 a 96.50 um para la sardina monterrey y de 60.60 a 62.50 um para la sardina crinuda. Esta morfologia del aparato filtrador se refleja en un mayor consumo de microplancton durante las fases adultas. Los taxa mas importantes en la dieta de ambas especies fueron Planktoniella sol y Coscinodiscus sp. (Bacillariophyceae), Peridinium sp. (Dinophyceae), con tamanos que variaron entre 75 y 150 um, asi como Calanus sp. (Copepoda), con tallas variables entre 700 y 1,500 um. Stomach contents and filtering apparatus of adult specimens of Pacific sardine (Sardinops caeruleus) and Pacific thread herring (Opisthonema libertate) from the Gulf of California were examined, in order to describe their feeding habits. Both species are omnivorous filter-feeders that present a wide trophic spectrum, showing high selectivity index values for some planktonic groups, whose frequency was directly proportional to their abundance in the plankton. The food overlap, in number as well as in volume, was found to be high between both species. The adults, compared to smaller-sized individuals, present very reduced gill raker gaps, of 90.20 to 96.50 um for Pacific sardine and 60.60 to 62.50 um for Pacific thread herring. This morphology of the filtering apparatus is reflected in a higher consumption of microplankton during the adult phase. The most important taxa in the diet of both species were P lanktoniella sol and Coscinodiscus sp. (Bacillariophyceae). Peridinium sp. (Dinophyceae), with sizes that ranged from 75 to 150 pm, as well as Calanus sp. (Copepoda), with variable sizes between 700 and 1,500 Pm.