Paddlefish (Polyodon spathula)

FishFreshwaterLiving fossil

Overview

Paddlefish (family Polyodontidae) are large, ancient freshwater fish instantly recognised by the long, flat, paddle-shaped snout (the rostrum) that extends from the front of the head. The American paddlefish (Polyodon spathula), shown here, is a smooth, scaleless, shark-like fish of the big rivers of central North America. Like sturgeons — their close relatives — paddlefish are survivors of a very old lineage, true “living fossils.”

Despite their size, paddlefish are gentle giants: they feed not by hunting but by filtering tiny plankton from the water, swimming with the mouth open like a living net, and they use the remarkable paddle to sense their prey.

Conservation note: the American paddlefish has declined from dams, habitat loss, and overfishing for its roe (caviar), and a second species (the Chinese paddlefish) is now considered extinct. Verify current status at authoritative sources.

Habitat & Range

The American paddlefish lives in the large, slow rivers and connected lakes and reservoirs of the Mississippi River basin and other central North American waters. It needs big, free-flowing rivers with the open water it filter-feeds in and the gravel-bar spawning sites it migrates to — needs that dams and river changes have disrupted.

Diet

Paddlefish are filter feeders that eat zooplankton — tiny drifting animals such as water fleas and copepods. A feeding paddlefish swims with its huge mouth gaping, straining plankton from the water with comb-like gill rakers, much like some sharks and whales do. They do not hunt or bite prey; their whole feeding apparatus is built for sieving the smallest food.

Behavior

The paddle is far more than decoration: it is covered in thousands of sensory receptors that detect the weak electric fields given off by swarms of tiny plankton, helping the paddlefish locate dense food in murky water where it cannot see. The fish then opens its mouth to filter the plankton as it swims through. Paddlefish are long-lived and slow to mature, and they undertake upstream migrations to spawn over gravel bars when river conditions are right — which is why barriers to migration hit them so hard.

Human Interaction & Conservation

Paddlefish have long been valued by people — for food and especially for their roe, sold as caviar — and this, together with the damming and alteration of their rivers, has driven serious declines. The American paddlefish is now managed and protected in much of its range, while the Chinese paddlefish was declared extinct, a stark warning about river-fish conservation. Restoring river connectivity is key. Consult authoritative sources for current status.

More photos of the paddlefish