Sturgeon are ancient fish species, often called “living fossils” due to their remarkable evolutionary stability. These creatures have navigated Earth’s waters for millions of years, largely unchanged since the Late Cretaceous period. Their enduring presence makes their appearance a subject of great interest.
Key Identifying Features
A defining characteristic of sturgeon is the presence of five rows of bony plates, known as scutes, which cover their bodies instead of scales. These scutes function as armor, offering protection from predators and environmental abrasions. While typically prominent, these bony plates can be quite sharp, especially in younger sturgeon. This unique dermal armor is a modified type of ganoid scale.
Another distinctive feature is the four sensitive, whisker-like barbels, located on the underside of their snout, just in front of their mouth. Equipped with taste buds, these sensory organs allow sturgeon to detect food in murky, low-visibility environments where they forage. They drag these barbels along the riverbed or seafloor, sensing chemicals, vibrations, and electrical fields from hidden prey.
Sturgeon have a mouth positioned on the underside of their head, which is toothless and highly protrusible. This specialized mouth can extend downward like a vacuum, enabling them to suck up food along with sediment from the bottom. After ingesting their meal, they can expel any inedible material like pebbles or sand.
Their tail fin is heterocercal, meaning its upper lobe is longer than the lower lobe. This asymmetrical tail structure is similar to that found in sharks and helps generate both lift and thrust as the fish swims. This design aids their movement and maneuverability near the bottom.
Overall Body Plan and Dimensions
Sturgeon typically have an elongated, cylindrical, or torpedo-shaped body, which appears smooth-skinned rather than scaled. This streamlined form is well-suited for navigating aquatic environments. While their back and sides are armored with scutes, the rest of their skin is generally smooth.
Their coloration often blends with their environment, commonly appearing as drab shades of bluish-black, olive brown, or grey on their dorsal (upper) side. Their sides tend to be paler, transitioning to a white or yellowish-white belly. This counter-shading helps them camouflage, making them less visible to predators from above against the dark bottom and from below against the lighter surface.
Sturgeon are recognized for their impressive size, with considerable variation among the 27 species. Many commonly reach 2 to 3.5 meters (7 to 12 feet) and weigh 180 to 360 kilograms (400 to 800 pounds). Some of the largest recorded individuals, such as the Beluga sturgeon, have measured up to 7.2 meters (23 feet 7 inches) long and weighed over 1,571 kilograms (3,463 pounds). These long-lived fish can survive for many decades, with some individuals living over 100 years.
Subtle Variations and Adaptations
While the general appearance of sturgeon is consistent, subtle variations exist among different species. For instance, snout shape can differ; some species like the Green sturgeon have a more pointed snout, while others, such as the White sturgeon, possess a blunter one. The arrangement and number of scutes can also vary slightly, and their sharpness tends to decrease as the fish ages.
These physical attributes are highly adapted to their bottom-dwelling, scavenger lifestyle. Their elongated snout, sometimes described as shovel-like, assists in stirring up substrate and sediments to uncover prey. The placement of their barbels and underslung mouth are perfectly suited for locating and consuming organisms found on or within the riverbed or lakebed. Their robust, armored bodies also provide protection in these environments.