Ontogenic diet shifts and scale-eating in Roeboides dayi, a Neotropical characid

Abstract

Scale feeding (lepidophagy) has been documented for a variety of Neotropical fish taxa, including the characid genus Roeboides. Ontogenetic differentiation of jaws and snout teeth allow larger Roeboides to remove scales, however, the less specialized tooth/jaw structure in Roeboides dayi, indicates that it may be a facultative scale feeder. Population dynamics and diets of R. dayi in a Venezuelan lowland swamp/creek and a piedmont stream were compared over an annual cycle. Juvenile R. dayi consumed aquatic insect larvae and microcrustacea, and although spawning was year-round at both sites, most reproduction occurred during the wet season when the availability of these resources was greatest for juveniles. At both sites, larger R. dayi fed on a combination of invertebrate prey and fish scales, the former being more important at the piedmont site, and the latter being especially important during initial low water conditions at both sites. In the lowland stream, the reduction of aquatic habitat during the early dry season created higher fish densities and a more profitable environment for scale-feeders. Insectivory probably was less profitable during this early low water period due to interspecific competition for reduced aquatic insect stocks.