Paddlefish

Paddlefish belong to the family Polyodontidae and order Acipensiformes. There are six known species—four are extinct (three from western North America, one from China) and known only from fossil remains, while two extant species include the paddlefish (Polyodon spathula), which is native to the Mississippi River basin in the United States, and the gigantic critically endangered Chinese paddlefish (Psephurus gladius) endemic to the Yangtze River Basin in China, where they lived primarily in the broad-surfaced main stem rivers and shoal zones along the East China Sea. Paddlefish are basal Chondrostean ray-finned fish; they are archaic and have been referred to as “primitive fish” because they have evolved with few unique morphological changes since the earliest fossil records of the late Cretaceous (seventy to seventy-five million years ago) of western North America.

Johan Julius Walbaum described the paddlefish in 1792, and it was a source of amazement to the first white explorers to the reach the Mississippi River Valley. Even before the formal description, in his 1758 History of Louisiana, the ethnographer, historian, and naturalist Antoine Simon le Page Du Pratz (1695–1775) provided an illustration of a specimen of P. spathula. In his famous 1787 work Notes on the State of Virginia, Thomas Jefferson (1743–1826) listed eleven species of fish, including the spathula fish (paddlefish).

Morphologically, the caudal fin of paddlefishes is strongly heterocercal (with unequal upper and lower lobes), the skeleton is almost entirely cartilaginous, scales are mostly absent (a small patch of ganoid scales can be found on the caudal peduncle), and eyes are minute. They also possess an extremely long, paddle-shaped snout covered with taste buds and two minute barbels on the underside. The gill cover extends back as a long, pointed flap (operculum). They also have a primitive spiral valve intestinal tract similar to that found in sharks. Paddlefish fry lack the distinctive adult paddle and retain teeth in their jaws as young juveniles, whereas adults are toothless but possess numerous, very long and slender gill rakers for straining food. Small paddlefish are pink on the dorsum and white on the venter, while larger individuals are bluish-gray (nearly black) on the dorsum and cream on the venter.

The North American paddlefish is an inhabitant of large, silty rivers, with populations also occurring in man-made reservoirs and the southern Great Lakes. Its overall native range includes the Mississippi River basin from New York to Montana, and south to the Gulf Coastal drainages from the Mobile Basin to the San Jacinto River in Texas. In Arkansas, P. spathula has been reported from large, low-gradient rivers such as the Arkansas, Mississippi, Ouachita, Red, and lower White, along with their major tributaries. It is sometimes found in oxbow lakes along the Arkansas side of the Mississippi River that periodically floods.

Paddlefish populations have declined dramatically since the mid-twentieth century throughout their historic range as a result of overfishing, pollution, and the encroachment of human development, including the construction of dams that have blocked their seasonal upward migration to ancestral spawning grounds. Other detrimental effects include alterations of rivers, which have changed natural flows resulting in the loss of spawning habitat and nursery areas, as well as harvesting for caviar. The species has been extirpated from much of its northern peripheral range, including the Great Lakes and Canada, Maryland, New York, and Pennsylvania. In Arkansas, P. spathula used to be much more widespread and common, and likely declining due to extensive damming of streams and other habitat alterations. The paddlefish is classified as vulnerable (VU) on the International Union for Conservation of Nature (IUCN) Red List, and its international trade has been restricted since June 1992 under Appendix II of the Convention of International Trade in Endangered Species of Wild Flora and Fauna (CITES). It is ranked S2 (imperiled) in Arkansas according to NatureServe.

Paddlefish commonly reach 1.5 m (5.0 ft.) or more in length and can weigh more than 27 kg (60 lbs.). The largest on record was taken by spear in 1916 in Okoboji Lake, Iowa, and measured 2.16 m (7 ft. 1 in.) long and weighed over 90 kg (198 lb.). The world record rod-and-reel-caught paddlefish weighed 65 kg (144 lb.) and was 1.4 m (54.3 in.) long, and was caught in a pond in Atchison County, Kansas. In Arkansas, a record 47.6 kg (105 lb.) paddlefish was taken by rod and reel from Beaver Lake in 2015.

The paddlefish is a long-lived (may reach fifty years), late sexually maturing species. For example, the females do not begin spawning until they are seven to ten years old, some even as late as sixteen to eighteen years old, whereas the males begin around age seven, some as late as nine or ten years of age. Females apparently do not spawn every year; rather, they spawn every second or third year, while males take part more frequently, typically every year or every other year. Paddlefish spawn in late spring, provided the combination of environmental parameters is optimal, including water flow, temperature, photoperiod, and availability of gravel substrates suitable for spawning. Paddlefish make upstream spawning runs and prefer silt-free gravel bars and riprap areas in swift water but will also utilize tailwater areas below dams. They are broadcast spawners, and gravid females release up to 500,000 eggs into the water over bare rocks or gravel at the same time males release their sperm. The eggs are adhesive and stick to the rocky substrate. The young are swept downstream after hatching and grow rapidly to adulthood in deep freshwater pools. However, as dams have blocked migratory corridors, and as off-channel habitats on many river reaches have disappeared or become disconnected, paddlefish reproductive success has declined, and paddlefish have increasingly used reservoirs for rearing.

Paddlefish jaws are distinctly adapted for filter feeding only. They are random suspension filter feeders with a diet that consists primarily of zooplankton (mostly cladocerans and copepods) and occasionally small insects, insect larvae (mayflies), and small fish. Paddlefish are indiscriminate feeders that also ingest detritus and sand along with their prey items. When feeding, this fish swims with its mouth gaping, straining small plankton and appropriately sized particles from the water with its gill rakers. Unlike popular fish lore among anglers, the paddlefish does not use its rostrum for rooting in substrate for feeding. Rather, for foraging, they possess electroreceptors on their bills to detect weak electrical fields of prey items in the water column. In addition to these electroreceptors, paddlefish also have sensory pores covering nearly fifty percent of the skin surface extending from the rostrum to the top of the head down to the tips of the gill flaps.

Paddlefish possess excellent flesh that is considered a delicacy when baked as fillets. In addition, their valuable raw roe (as caviar) is converted into a high-quality, ready-to-eat finished product, and recently has been utilized heavily by commercial demand—so much so that this fish has received considerable attention by fishery biologists with an eye toward fish farming. According to chef Wolfgang Puck, paddlefish eggs have been commercially available for more than a century, though traditionally they have been shunned by connoisseurs. But the commercial demand has been increasing greatly in recent years due to collapse of beluga (Huso huso) and other Caspian Sea sturgeons. Paddlefish caviar has been increasingly accepted as a high-quality replacement in many domestic and international (mainly European and Japanese) markets. In addition, China has also exported paddlefish to Cuba, where they are farmed for caviar production.

Commercial catch of P. spathula is permitted in seven states, including Arkansas, Alabama, Illinois, Kentucky, Mississippi, Missouri, and Tennessee. In 1992, the largest volumes of commercial catch were recorded in Arkansas (sixty-five percent, or 136,000–181,000 kg) and Tennessee (twenty-five percent, or 60,328 kg), with the remaining ten percent shared by Illinois (21,145 kg), Kentucky (3,906 kg) and Missouri (2,188 kg). Commercial harvest of P. spathula in 1992 was estimated at 136 to 181 tons. From 1990 to 1999, the Arkansas Game and Fish Commission (AGFC) collected $150,000 to $300,000 annually in revenues for the sale of commercial and paddlefish sport fishing licenses, permits, and tags. However, there was no compulsory system for reporting commercial catch data to the authorities in Arkansas. Based on voluntary reporting of commercial fisheries, a total of 69 kg of paddlefish roe was harvested in 1998 (out of a total catch of paddlefish estimated at 410 kg), while 230 kg average annual harvest of caviar (worth $16,256) had been reported for 1987 and 1988. More recently, restrictions on the take of paddlefish and their eggs were implemented by the AGFC. In 2017, it was unlawful to take, sell, or possess paddlefish or sturgeon, or their parts (including eggs) without a current resident roe taker/seller permit, which requires a commercial fishing license. By 2018, the daily creel limit for paddlefish in Arkansas had been set at two per day.

Recent advancements in biotechnology for paddlefish propagation and rearing of captive stock indicate significant improvements in reproduction success, adaptation, and survival rates of paddlefish cultured for broodstock development and stock rehabilitation. Such improvements have led to successful practices in reservoir ranching and pond rearing, creating an increasing interest in the global market for paddlefish polyculture. For example, the Paddlefish Research Center (PRC), part of the Oklahoma Department of Wildlife Conservation located in Miami, Oklahoma, collects data on each specimen’s sex, weight, length, age, and health in an attempt to manage this unique fish. Fishermen are encouraged, but not required, to hand over both sexes of paddlefish to the PRC. In return, fish are filleted, packaged, and returned to the angler for free, but the center keeps all of the roe. This roe is then processed into caviar, with the proceeds of sales going toward fish and wildlife resource conservation, management, and enforcement activities. This results in high-quality scientific data used to help manage P. spathula in the state, and the paddlefish research and stock assessment activity has increased significantly in the name of conservation.

Paddlefish have been imported into Russia for aquaculture, and they were introduced into several rivers in Europe and Asia. Paddlefish are now being raised in several other European countries, including Austria, Bulgaria, the Czech Republic, Germany, Hungary, Romania, and Serbia.

Chinese paddlefish (sometimes called “Elephant Fish”) have not fared as well as P. spathula and have not been observed in the wild since 2007. The most recent specimen was captured by illegal fishing on January 8, 2007, in Jiayu County and measured 3.6 m (12 ft.), 250 kg (550 lb.). In addition, during a search conducted between 2006 and 2008, a team of researchers from the Chinese Academy of Fisheries Science failed to see any paddlefish. They may now be extinct due to many of the same hazards that have beset P. spathula. Past attempts of artificial propagation for restoration purposes have failed because of difficulties encountered in keeping captive fish alive.

There are few reported natural predators of paddlefish. Bighead carp, an invasive species, are present in Arkansas and can compete for food with juvenile paddlefish. Sauger and walleye have been reported to feed on small paddlefishes in North Dakota. Parasites of P. spathula include protists, cnidarians, monogeneans, trematodes, cestodes, nematodes, leeches, and crustaceans.

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Chris T. McAllister
Eastern Oklahoma State College