Paddlefish

Scientific name: Polyodon spathula

Country: United States of America

Continent: North America

Diet: Zooplankton and aquatic larvae

Food & feeding: Zooplanktivore (filter feeder).

Habitats: Freshwater.

Conservation status: Vulnerable.

Relatives: Chinese paddlefish and sturgeon.

Description: Paddlefish are large fish that can grow up to 1.5 m and weigh 80 kg. Despite its cartilaginous skeleton, it is not closely related to sharks, being grouped with sturgeons and gar fish. Its body is almost entirely without scales and it is characterised by its elongated flatted snout. This snout or ‘rostrum’ can be as much as 50% of the body length and it is covered in electroreceptors. It has a large mouth with gill rakers (bony projections of the gills that sieve out food particles from the water) for filter feeding. This creature is known as a ‘fossil fish’, being virtually unchanged from its ancestors, fossils of which date back to the Cretaceous Period, 145 to 65 million years ago.

Lifestyle: Paddlefish are found only in the lakes and slow flowing rivers of the Mississippi and its tributaries. As a passive filter feeder it constantly swims along rivers, moving long distances close to the water surface in search of food. The snout or ‘paddle’ acts as an antenna, detecting the electric impulses given off by the zooplankton. It then cruises through the clouds of tiny animals with their mouths gaping, straining out the food particles through their comb-like gill rakers. Being able to detect electrical fields means that paddlefish can happily feed in total darkness.

Family & friends: Paddlefish are usually solitary, except at breeding time and as larvae.

Growing up: Spawning occurs in the spring, after adults have migrated upstream to their favoured breeding site. Eggs are adhesive and are laid midstream, sticking to rocks and pebbles. Once hatched, the larvae are washed down to deep feeding pools. Females mature at about ten years, at a length of 105 cm; males mature earlier at seven years (100 cm). Paddlefish can live to over thirty years old.

Conservation news: This vulnerable species is under threat from over fishing for meat and roe (eggs) for the delicacy caviar. Habitat disturbance also affects this fish, with large dams interrupting their spawning migration routes. Bristol Zoo is the only UK collection to have this species.