Shad are a group of fish belonging to the herring family, Clupeidae, known for their migratory patterns between marine and freshwater environments. This article will detail the general appearance of shad, followed by specific features that aid in their identification.
Physical Description
Shad possess a body form that is typically thin and metallic, appearing deep-bodied and compressed from side to side. For instance, the American shad, a prominent species, commonly reaches lengths between 19 and 24 inches, weighing approximately 3 to 8 pounds. Some individuals can grow larger, with reported maximums reaching up to 30 inches in length and weighing as much as 12 pounds. Female shad generally attain greater sizes than males.
The coloration of shad often features a dark blue or greenish hue along their backs, transitioning to bright silvery sides. Their underbellies are typically white, creating a contrast that helps them blend into their aquatic surroundings. It is worth noting that their colors can sometimes darken to a more brownish shade when they enter freshwater environments for spawning.
Regarding their fin structure, shad typically have a single dorsal fin positioned centrally on their back. Their tail fin, known as the caudal fin, is deeply forked, providing efficient propulsion through water. They also possess pectoral, pelvic, and anal fins, which contribute to their stability and maneuverability.
Shad are characterized by their large, cycloid scales, which are smooth-edged and often shed easily. A distinctive feature is the presence of sharp, saw-like scales, or “scutes,” along their bellies. These scutes form a prominent keel along the underside of their body.
The head of a shad generally presents with a blunt snout. While young shad may have small teeth, adult shad are largely toothless. The overall mouth structure tends to be small, although its specific configuration can vary among different shad species.
Unique Identifying Features
A common identifying mark for the American shad is a single, large dark spot located just behind the upper part of their gill cover, also known as the operculum. This primary spot is often followed by a horizontal row of smaller, fainter spots along the upper side of their body. In some instances, a second or even a third row of these smaller spots may be present.
The American shad has a mouth where the lower jaw fits neatly into a V-shaped notch in the upper jaw when closed. This differs from the hickory shad, which is identified by its noticeably protruding lower jaw, creating an underbite. Conversely, the gizzard shad possesses a small, toothless mouth that is positioned subterminally, meaning it is located on the lower portion of the head, and its upper jaw is short and wide with a deep notch.
Another distinguishing characteristic found in gizzard shad is an elongated, filament-like last ray of their dorsal fin. Threadfin shad also exhibit an elongated dorsal fin ray, which extends like a trailing thread. Their mouth is more terminal, positioned at the front of the head without a projecting upper jaw, and their caudal fin often has a yellowish tint. These detailed features allow for more precise identification of shad species.