Meeting Abstract
Fin evolution has allowed for the diversification of fish morphology and subsequent exploration of new habitats. Basal bony fishes have elongated body shapes where paired fins contribute little to thrust. Instead caudal fin and body undulation are the main propellers for these species, although the diversity of dorsal and anal fin shapes seems to indicate a functional role of all the median fins in swimming. Sturgeons are unique in the retention of the notochord in the upper lobe of the caudal fin, which is even more pronounced and elongated in juvenile individuals. We focus on captive bred juvenile pallid sturgeon, an endangered species endemic to the basins of the Missouri and lower Mississippi, to examined median fin function during steady swim in a flow tank using high speed videography and PIV. Our kinematic data show that sturgeon undulate the dorsal and anal fins slightly out of phase with each other, reflecting the dorsal fin’s slightly anterior position in respect to the anal fin. These two fins also move with a considerable phase shift to the caudal fin. In terms of lateral displacement, as expected, the lower lobe of the caudal fin has the highest range of motion, almost double that of the dorsal fin. Considering their similar sizes, the higher range of motion of the anal fin in comparison to the dorsal fin is rather surprising. PIV data show evidence of vorticity indicative of thrust generation behind the dorsal fin that is likely to interact with the tail. It also seems to suggest that the elongated upper lobe functions as a trailing edge for vortex redirection. Understanding how endangered species interact with their habitat can aid in effective conservation efforts. Furthermore this study supports the relevance of median fin function not solely explained by the caudal fin and supports the diversification of fin shape with evolutionary implications.
