Paddlefish

Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to the order Acipenseriformes, one of two living groups within this order alongside sturgeons (Acipenseridae). Their most distinctive feature is an elongated rostrum that enhances electroreception, allowing them to detect prey in murky water. Often called "primitive fish," paddlefish represent one of the earliest diverging lineages of ray-finned fish, having separated from all other living groups over 300 million years ago. Both living and fossil paddlefish occur almost exclusively in North America and China.

Eight species are known, six of which survive only as fossils—five from North America and one from China. Of the two extant species, the American paddlefish (Polyodon spathula) inhabits the Mississippi River basin in the United States, while the Chinese paddlefish (Psephurus gladius) was declared extinct in 2022 following a 2019 recommendation. The last confirmed sighting of a Chinese paddlefish occurred in the Yangtze River Basin in 2003. The Chinese paddlefish is also known as the "Chinese swordfish" or "elephant fish." The earliest known paddlefish fossil, Protopsephurus, dates to approximately 120 million years ago during the early Cretaceous (Aptian) period in China.

Throughout their historic range, paddlefish populations have declined dramatically due to overfishing, pollution, and human development. Dam construction has proven particularly destructive, blocking seasonal migrations to ancestral spawning grounds. River alterations have changed natural flow patterns, destroying spawning habitat and nursery areas critical to population survival.

Paddlefish are among the few organisms that retain a notochord beyond the embryonic stage. Their bodies contain very few bones, consisting primarily of cartilage with the notochord serving as a flexible spine. During early development from embryo to fry, paddlefish lack a rostrum (snout), which begins forming shortly after hatching.

The rostrum shape varies dramatically between species. The Chinese paddlefish possessed a narrow, sword-like rostrum, while the American paddlefish displays a broad, paddle-shaped one. Both species share several morphological features: a spindle-shaped body with smooth, scaleless skin, a heterocercal tail, and small, poorly developed eyes.

The two species employed vastly different feeding strategies. Unlike its filter-feeding American relative, the Chinese paddlefish was a piscivore—a highly predatory fish. Its forward-pointing jaws suggest it hunted primarily for small fish in the water column, supplementing its diet with shrimp, benthic fishes, and crabs. In contrast, the American paddlefish jaw is specialized exclusively for filter feeding. As ram suspension filter feeders, they consume primarily zooplankton, occasionally taking small insects, insect larvae, and small fish.

The largest recorded Chinese paddlefish measured 23 ft (7.0 m) in length and was estimated to weigh several thousand pounds. More commonly, these fish reached 9.8 ft (3.0 m) and 1,100 lb (500 kg).

Though the American paddlefish ranks among the largest freshwater fishes in North America, it falls short of its Chinese cousin's impressive dimensions. American paddlefish commonly exceed 5 ft (1.5 m) in length and 60 lb (27 kg) in weight. The largest specimen on record was speared in 1916 in Okoboji Lake, Iowa. This fish measured 7 ft 1 in (2.16 m) long with a girth of 45.5 in (1.16 m). According to a 1969 report by J.R. Harlan and E.B. Speaker in Iowa Fish and Fishing, it weighed over 198 lb (90 kg).