Dietary histories of herbivorous loricariid catfishes: evidence from delta C-13 values of otoliths

The ecology of many Neotropical fishes is difficult or often impossible to study during rainy seasons. Thus, ecological studies of tropical fishes are usually performed on fish captured only during dry seasons. Because otoliths preserve a record of life history, this study evaluated the utility of otolith stable isotope values for the investigation of trophic ecology of Neotropical fishes (specifically herbivorous loricariid catfish) throughout their lives. Because plant dietary materials have delta C-13 values that are determined by their photosynthetic pathways, metabolism and environmental conditions, different plants may impart different isotope values on fish otoliths that reflect consumption of these plants. The delta C-13((otolith)) values of xylophagous Panaque nigrolineatus captured in the field were significantly lower than those of algivorous Hypostomus regani from a nearby region. A laboratory experiment wherein Hypostomus sp. had delta C-13((otolith)) values that reflected the delta C-13 values of their plant diet and additional evidence indicate that delta C-13((otolith)) values in loricariid catfish otoliths can record dietary history.