Meeting Abstract
Triggerfishes (Balistidae) and filefishes (Monacanthidae) power locomotion using their median dorsal and anal fins in a unique swimming mode termed balistiform locomotion. Balistoid fishes lie on a morphological continuum from fishes possessing median fins of low to high aspect ratio (AR) and a biomechanical continuum from fishes powering locomotion with broad oscillations to precise undulations of the median fins. Hydrodynamic theory and experimental evidence from other groups of fishes predict that fishes using fins of higher ARs for propulsion should be capable of higher critical swimming performance, a measure of endurance swimming capacity. We calculated ARs of dorsal and anal fins in balistoid fishes and performed phylogenetic ancestral state reconstructions to reveal that both high and low AR median fins evolved multiple times within Balistoidea. Additionally, filefishes tend to have lower AR median fins than triggerfishes. We predicted that critical swimming performance decreases with AR among multiple balistoid lineages and that swimming performance of filefishes decreases relative to triggerfishes. In order to investigate the performance consequences of evolutionary shifts in median fin shape, we performed critical swimming tests on morphologically and phylogenetically diverse balistoid species. Preliminary results for 11 balistoid species show that increasing median fin AR is associated with higher critical swimming performance (PGLS: p = 0.0024). Critical swimming speed is a key performance metric that may have influenced the evolution of balistoid median fin shape, although there may be additional performance metrics in which possessing lower AR median fins may be advantageous.
