Meeting Abstract
Although rare within the context of 30,000 species of extant ray-finned fishes, scale-feeding has evolved repeatedly across this branch of the tree of life. Scale-feeding (lepidophagous) fishes are diverse in terms of their ecology, morphology, and behavior, using strategies such as mimicry and ambush tactics, coupled with specialized cranial morphologies to graze off the scales and mucus of sympatric species. We examined the ontogeny of feeding mechanics in two scale-feeding characiform fish lineages: Roeboides, a characin, and Catoprion, a piranha. We compared these two scale-feeding specialist taxa to their nearest, non-lepidophagous taxa to identify traits held in common among scale-feeding fishes. We use a combination of micro-computed tomography scanning and iodine staining to measure biomechanical predictors of feeding behavior such as tooth shape, jaw lever mechanics, and jaw musculature. We recover a stark contrast between the feeding morphology of scale-feeding and non-scale-feeding taxa. Lepidophagous fishes display paedomorphic characters through to adulthood, such as a stout teeth and a small jaw muscles. However, few traits are shared between lepidophagous characins and piranhas, except for their paedomorphic, highly-modified, stout dentition. We suggest these robust teeth are critical to resisting the impact incurred when these scale-feeders pry or dislodge scales from prey during ram-feeding. Lepidophagous taxa are prime examples of equifinality in explaining the diversity of form and function across teleost fishes: there are many ways to adapt to the scale-feeding niche.
