Unusual relicts: New fish attract visitors’ attention
Relict newcomers have recently been added to the Rivers and Lakes exhibit. Unusually looking paddlefish Polyodon spathula, closely related to sturgeons, now live together with the inhabitants of the middle reaches of the Amur River. This species is the only extant member of the family Polyodontidae, which dates back 125 million years, and it has undergone little change during all this time. Paddlefish got its name due to a long rostrum resembling a paddle. It extends nearly one-third its body length and is used for detecting food.
“Paddlefish can grow in nature up to two metres. Our fish are young, about 30 cm long from the tip of a rostrum to the tip of a tail. We’ve lodged them now together with the fish that aren’t aggressive to them, but later we plan their relocation to the aquarium with large sturgeons and kalugas to expand our collection of Acipenseriformes, a taxonomic order that includes sturgeons and paddlefish,” explains Anna Kozmina, Head of the Department of the Russian Far East Freshwater Organisms. “Both paddlefish and bighead carps, their current neighbours, are plankton-eaters, and it is easier to feed and keep them together for the time being. Their food is a cocktail of spirulina, copepods, rotifers, and brine shrimp nauplii, all of which are grown at the Primorsky Aquarium.”
All fishes feeding on plankton have gills specifically accommodated for straining small organisms from the water. However, the sieve-like apparatus of paddlefish is a more advanced adaptation than in many other filter-feeders: it can expand similarly to a Hoberman sphere, thus considerably enlarging the area of straining.
Paddlefish are native to the Mississippi River in North America. They are successfully cultivated in the Far Eastern fish farms and may sometimes escape to be found in our lakes and rivers, where they can survive quite well.
General information:
— The maximum lifespan of paddlefish is 56 years.
— Paddlefish is listed as Vulnerable on the IUCN Red List. Its close relative, Chinese swordfish, had been for years considered Critically Endangered and in 2020 was reported to be extinct.
— Paddlefish females do not spawn every year. Reproduction cycles may occur once in four to seven years.