The unique appearance of sawfish, particularly their distinctive saw-like snout, often leads to confusion about their biological classification. Many people mistakenly believe these animals are sharks due to their overall body shape and powerful presence in marine environments. Understanding their true biological identity involves examining their specific anatomical features and correct classification within cartilaginous fish.
Understanding Sawfish
Sawfish are a type of ray, not a shark, despite their shark-like body. They belong to the class Chondrichthyes, which includes all cartilaginous fish, but are specifically classified within the superorder Batoidea, encompassing rays and skates. This classification places them as close relatives to stingrays and guitarfish.
A defining characteristic is their elongated, flattened rostrum, or “saw.” This extension is lined with sharp, transverse structures, which are modified dermal denticles. Sawfish use this saw for various purposes, including stunning schooling fish by slashing it side-to-side and digging in the seabed to dislodge invertebrates.
Sawfish have a flattened body, aiding their bottom-dwelling lifestyle. Their mouth and nostrils are positioned on the ventral (underside) surface of their head. Behind each small eye, they have a spiracle, which is a specialized opening used to draw water over their gills, particularly when they are resting on the seafloor or partially buried in sediment. Their five pairs of gill slits are also located on the underside of their body, near the base of their wing-like pectoral fins. These pectoral fins are broad and fused to the sides of their head and trunk, forming a continuous body outline.
Sawfish inhabit a variety of environments, from shallow coastal marine waters and estuaries to freshwater rivers and lakes. Some sawfish species can grow to impressive sizes, reaching lengths of up to 7.6 meters (25 feet) and weighing over 1,000 pounds. They are generally found in tropical and subtropical regions worldwide. While primarily bottom feeders, their specialized rostrum allows them to hunt fish and crustaceans in their diverse habitats.
Key Differences from Sharks
A primary distinction between sawfish (rays) and true sharks lies in the placement of their gill slits. Sawfish, like all rays, have their five pairs of gill slits located ventrally, on the underside of their body. In contrast, sharks typically have their five to seven gill slits positioned laterally, along the sides of their head.
The overall body shape also provides a clear differentiating feature. Rays, including sawfish, generally exhibit a flattened body profile. Most sharks, however, possess a more streamlined, torpedo-shaped body that is adapted for efficient swimming through the water column.
Pectoral fins also differ. In sawfish and other rays, these fins are greatly enlarged, wing-like, and fused directly to the head and body, forming a distinct disc shape. Sharks, conversely, have separate, distinct pectoral fins located behind their head, which function primarily for steering, lift, and stabilization during swimming.
The position of the mouth also varies. Sawfish and other rays have their mouths located on the underside of their head, adapted for feeding on prey found on the seabed. While some sharks also have subterminal mouths, many possess mouths positioned more towards the front or tip of their snout.
Regarding respiration, rays and certain bottom-dwelling shark species utilize spiracles, small openings behind their eyes, to draw water over their gills. This adaptation allows them to breathe even when their mouth is buried or at rest. Many active, open-water sharks, however, often lack prominent spiracles and rely on “ram ventilation,” where they must continuously swim forward to force water over their gills for oxygen exchange.