Feeding of Paddlefish, Polyodon spathula

The food of adult paddlefish, Polyodon spathula, from a section of the Missouri River (South Dakota-Nebraska) in 1975-76 was almost entirely crustacean zooplankton. Paddlefish were indiscriminate filter feeders and apparently ingested all material strained from the water column; organisms less than about 0.20-0.25 mm long (0.10-0.12 mm wide) were not retained. Detritus and sand averaged over 50% of the stomach contents by volume. Feeding peaked in spring and fall and ceased from late June to early September. Food intake did not change perceptibly over a 24-h period. Gill rakers begin to appear along gill arches when fish reach 65 mm eye-to-fork length (EFL) and are thought to become fully functional when fish reach 225250 mm (EFL). The interraker distance was not significantly different between gill rakers on the same gill arch; gill raker width varied. The relationship between fish length (EFL) and interraker distance (I) near the base of the gill rakers was I = 3.4 x 10-5 EFL + 0.035. The mean mesh size for fish 139-855 mm (EFL) ranged from about 0.06-0.09 mm. Our results are consistent with a hypothesis that assumes paddlefish have a non-sticky filter for which particle retention may be moderately altered.