Gill raker variation and the feeding niche of some temperate and tropical freshwater fishes

Synopsis Variability in the mean number of gill rakers was examined in 17 tropical (Panama) and 16 temperate (Canada) freshwater fishes. Ranges for an additional 16 temperate species were obtained from the literature. Variance in gill raker number within species was significantly greater in the tropical species. The tropical species also showed significantly greater dispersion of the species means when among-species variation was compared to an overall mean for each latitude. The reduced among-species variation observed in the temperate species appears to result from a scarcity of high raker means in small, stream species of Canada. This study offers no evidence for the existence of greater feeding specialization among small, primarily stream fishes in the neotropics. The data suggest that the food resource spectrum utilized by these species may be shorter at the higher latitudes examined.