9781934874127-ch10

Paddlefish Management, Propagation, and Conservation in the 21st Century

Morphological Variation in Juvenile Paddlefish

Jan Jeffrey Hoover, Krista A. Boysen, Catherine E. Murphy, and Steven G. George

doi: https://doi.org/10.47886/9781934874127.ch10

Abstract.—Juvenile paddlefish Polyodon spathula exhibit conspicuous variation in the shape of their rostra and caudal fins. We quantified morphological variation for a composite collection of young-of-year paddlefish (N = 55; 61.9–403.7 mm total length) using nine measurements of the rostrum, body, and caudal fin. Sheared principal component analysis of morphological data resulted in three distinct groups of fish corresponding to three different localities: hatchery-reared fish from the Mermentau River, Louisiana; hatchery-reared fish from the Tombigbee River, Alabama; and field-collected fish from the Mississippi River, Mississippi. Series were segregated from each other based on size of caudal lobes and width of rostrum. With increased body size of fish, relative length of rostrum increased, and mesal expansion of rostrum increased for all three series. For Tombigbee and Mississippi River series, with increased size of fish, caudal asymmetry decreased. Overall, smaller fish had shorter, narrower rostra and highly asymmetrical caudal lobes; larger fish had longer, broader rostra and more symmetrical caudal lobes. Morphological differences among series were most conspicuous for fish greater than 85 mm eye-to-fork length. Fish from Mermentau River had shorter, narrower (leaf-shaped) rostra and asymmetrical (conspicuously heterocercal) caudal lobes. Those from the Tombigbee River had longer, broader (spoon-shaped) rostra and more symmetrical caudal lobes. Those from the Mississippi River had the longest, broadest (paddle-shaped) rostra and symmetrical (superficially “homocercal”) caudal lobes. Locality-based gradient in paddlefish morphology corresponds to a gradient in river hydrology: longer, broader rostra and symmetrical caudal lobes were associated with larger basins, higher gradients, and greater discharge.