ULTRASONOGRAPHIC GENDER DETERMINATION IN THE PADDLEFISH
POLYODON SPATHULA.

Robert O'Brien1, Joanne Paul-Murphy1, and Mark Steingraeber2
1Department of Surgical Sciences, School of Veterinary Medicine, University of
Wisconsin-Madison, Madison, WI 53706 2Fisheries Resource Office, U.S. Fish and
Wildlife Service, Onalaska, WI 54650.

The use of ultrasonography as a tool to determine gender of the paddlefish Polyodon
spathula  was investigated. Paddlefish were captured by net in the Chippewa River as part
of a project on telemetry. Fourteen fish were imaged in dorsal recumbency with a 5 MHz
linear transducer and portable ultrasound system. Organs that were well characterized in
every fish were heart, liver, stomach, spiral valve, gonad and spleen. The egg mass in
gravid female fish was located in the ventral coelom and very sound attenuating, resulting
in a characteristic hyperechoic (bright) near-field interface with rapid decrease in signal
intensity becoming hypopechoic (dark). The testes were located dorsolaterally in the mid-
to caudal coelom and ultrasonographically nonattenuating, hyperechoic, and L-shaped in
transverse images. No nongravid females were identified with ultrasound. The gender was
verified in six fish by laparotomy. Ultrasonography is a sensitive method to rapidly
determine gender in gravid female paddlefish. The appearance of gonads in nongravid
females, to distinguish from males, requires further study.

Keywords: paddlefish, Polyodon spathula , ultrasonography







1. Robert O'Brien 2015 Linden Drive West, Madison, WI 53706
2. platform (yes)
 3. no