TROPHIC ORGANIZATION OF MOJARRAS (PISCES, GERREIDAE) AT CIENAGA-GRANDE-DE-SANTA-MARTA (CARIBBEAN OF COLOMBIA)

The feeding habits of the eight species of mojarras (Gerreidae) occurring at the Cienaga Grande de Santa Marta are described. Three methods were used to analyze the food eaten by 365 specimens: gravimetric, frecuency of ocurrence and a relative importance index. Mojarras are omnivorous and euriphagous fishes, eating a wide spectrum of items, mainly small invertebrates (bivalves, gastropods, ostracods, copepods, polychaetes) taken on the oyster banks located inside the Cienaga and on the sand-muddy bottoms near the mouth of the lagoon. Intraspecific competition seems to be lowered as a consequence of the spatial segregation of the populations and the diel variation of the food items. Percentage of replenished stomachs increases in the high salinity period. The usefulness of the various food analysis methods is compared, and the frecuency of occurrence method is recommended for this group.