What Is the Difference Between Paddlefish and Sturgeon?

Paddlefish and sturgeon are often called “living fossils” due to their ancient lineage. Their large sizes and distinct body shapes hint at a history that stretches back to the time of the dinosaurs. These fish inhabit large river systems where their prehistoric forms are distinctive, and exploring their similarities and differences reveals a story of evolution.

An Ancient Family Connection

The relationship between paddlefish and sturgeon is that of evolutionary cousins. Both belong to a group of ray-finned fish called Acipenseriformes, which has a fossil record dating back to the Jurassic Period. This shared ancestry means they possess primitive characteristics, such as skeletons made mostly of cartilage rather than bone.

Despite this shared heritage, they occupy separate branches on the family tree. The order Acipenseriformes is divided into two distinct families: the paddlefish belong to Polyodontidae, while sturgeons are in the family Acipenseridae. Genetic analysis suggests these two families diverged 114 to 184 million years ago. There are 25 recognized species of sturgeon, whereas only one species of paddlefish remains in North America, with another in China now considered extinct.

Distinguishing Physical Features

The most apparent difference between paddlefish and sturgeon lies in their snouts. The American paddlefish is named for its defining feature: a long, flattened, paddle-shaped rostrum that can make up one-third of its total body length. This structure is not a weapon but a sensory organ covered in electroreceptors that detect the electrical fields of prey.

In contrast, sturgeons have snouts that are cone-shaped or shovel-like, varying by species. Below their snouts, sturgeons have four whisker-like sensory organs called barbels, which they drag along the riverbed to detect food.

Another distinguishing feature is their skin and body armor. Sturgeons are famous for the five rows of bony plates, called scutes, that run along their bodies, giving them an armored appearance. Paddlefish, however, have smooth, scaleless skin, which makes them appear similar to sharks or catfish.

The mouths of these fish are also adapted to their different lifestyles. A sturgeon’s mouth is located on the underside of its head and is protrusible, meaning it can extend to suck up organisms from the river bottom. Paddlefish have a large, gaping mouth that is not protrusible.

Feeding Habits and Habitat

The physical adaptations of paddlefish and sturgeon directly influence their feeding behaviors and where they live. Paddlefish are primarily filter-feeders. They swim continuously through the water with their large mouths open, straining water through their gill rakers to capture zooplankton and insect larvae. Their paddle-like rostrum helps them locate dense patches of this microscopic prey.

Sturgeons are bottom-feeders, using their sensitive barbels to explore the mud and gravel of riverbeds for invertebrates like insects, worms, crustaceans, and mollusks. Once prey is detected, they use their extendable, suction-like mouths to ingest it.

While both fish are found in large freshwater river systems across the Northern Hemisphere, their lifestyles can differ. The American paddlefish lives exclusively in freshwater rivers, such as the Mississippi River basin. Many sturgeon species, however, are anadromous, meaning they spend much of their adult lives in saltwater and migrate upstream into freshwater rivers to spawn.

The Prized Roe and Conservation Status

Both paddlefish and sturgeon are highly valued for their eggs, which are processed and sold as caviar. This has made them a target for overfishing and poaching, putting immense pressure on their populations and driving their decline. This fishing pressure, combined with other threats, has led to a perilous conservation status for both groups.

According to the International Union for Conservation of Nature (IUCN), nearly all remaining species of sturgeon and paddlefish are threatened with extinction, making them one of the most endangered groups of animals on the planet. The Chinese paddlefish was officially declared extinct, and many sturgeon species are now listed as critically endangered.

Conservation efforts are complicated by environmental changes. The construction of dams blocks their migratory routes to spawning grounds, and water pollution degrades the quality of their habitats. In response, conservation programs are working to restore habitats, implement fishing regulations, and operate hatcheries to restock depleted populations.