Shad, a herring family fish, are known for their anadromous life cycle: spending most of their lives in saltwater and migrating to freshwater rivers to spawn. As the largest member of the herring family, American shad (Alosa sapidissima) are a notable species found along the Atlantic coast of North America. This overview focuses on the observable features that characterize shad, providing insight into their distinctive form and markings.
Key Physical Characteristics
Shad possess a slender, elongated body that is laterally compressed, appearing flattened from side to side. Their streamlined shape aids in efficient movement through water, contributing to their quick swimming abilities. Adult American shad typically measure 20 to 24 inches (50 to 60 centimeters) in length, though some reach 30 inches (75 centimeters). Females generally grow larger than males, commonly weighing 8 pounds, though some reach 12 pounds.
The coloration of a shad is striking, featuring shiny silver sides that blend into a darker, often bluish-green or greenish-blue, back. This metallic luster provides a natural camouflage in their aquatic habitats. Their scales are large, cycloid, smooth-edged, and shed easily. This characteristic is common among many herring species.
Shad have a single dorsal fin positioned slightly forward of the body’s midpoint. Their caudal fin, or tail fin, is deeply forked, providing significant propulsion for swimming. The anal fin is relatively short and located well behind the base of the dorsal fin, while the pelvic fins are situated towards the chest region of the fish. The head is proportioned to the body, leading to a terminal mouth where the upper and lower jaws meet at the front. Adult shad are toothless, though very small teeth may be present in juveniles.
Identifying Marks
A distinguishing feature for many shad species, particularly the American shad, is the presence of dark spots along their sides. There is typically a prominent dark spot located directly behind the upper part of the gill cover (operculum). This main spot is often followed by a series of smaller, sometimes fainter, spots extending backward along the upper flank. In some instances, a second, or even a third, row of these smaller spots may be visible below the primary row.
Another key identifying characteristic is the row of bony, saw-like projections known as scutes, which run along the midline of the shad’s belly from the throat to the anal fin. These sharp-edged scutes create a distinct keel along the underside of the fish. When touched, these scutes can feel spiny and are a reliable way to identify shad within the herring family. The jaw structure also provides a specific cue, as the upper jaw of a shad features a noticeable median notch into which the tip of the lower jaw fits precisely when the mouth is closed. This particular jaw alignment differentiates shad from other similar-looking fish, such as the hickory shad, which typically has a lower jaw that protrudes beyond the upper jaw.