The Alaska Pollock, scientifically known as Gadus chalcogrammus, is an important commercial fish species found in the North Pacific Ocean, particularly the Bering Sea. Due to its smooth appearance, the fish is often misidentified as being scaleless. However, the Alaska Pollock possesses a full covering of scales across its body. This integumentary layer offers protection and influences its hydrodynamic efficiency in the marine environment.
Scale Presence and Type
The scales of the Alaska Pollock are classified as the cycloid type, commonly found among bony fishes. These cycloid scales are small, thin, and smooth, lacking the comb-like teeth or spines found on ctenoid scales. The term “cycloid” refers to their circular or rounded shape and smooth posterior margin.
A defining feature of the scales is their minute size and the fact that they are deeply embedded within the skin. This embedding, combined with their small size, is the primary reason the fish feels slick and appears scaleless when handled. The scales are also brittle and easily damaged, which further contributes to the perception that they are not present.
Cycloid scales allow for greater body flexibility compared to other scale types, which is beneficial for a schooling fish like the Alaska Pollock. This smooth, flexible coating helps reduce drag as the fish moves through the water, allowing for more energy-efficient swimming. Biologists utilize these scales because they form concentric growth rings, or annuli, which can be counted to estimate the age of the fish.
Taxonomic Placement of Alaska Pollock
The presence and nature of the Alaska Pollock’s scales are consistent with its position in the biological classification system. It belongs to the order Gadiformes, a large group of fishes known as the cods and their relatives. Gadiformes typically feature smooth, elasmoid cycloid scales and generally lack fin spines.
The species is further classified into the family Gadidae, the true cods, alongside species like the Atlantic Cod and Pacific Cod. For a long period, Alaska Pollock was placed in its own genus, Theragra, but genetic research confirmed its close relationship to the true cods, leading to its reclassification into the genus Gadus. This taxonomic placement means the minute, cycloid scales are a characteristic shared among the family members.
The small, smooth scales are a standard feature for a member of the Gadus genus within the larger Gadidae family. Understanding this classification provides context for why the scales are present but so inconspicuous on the fish’s body.
Defining Anatomical Features
Beyond the scales, the Alaska Pollock exhibits several other distinct anatomical features that identify it as a member of the cod family. A prominent feature is the arrangement of its fins, which includes three separate dorsal fins along its back. These fins are widely spaced and separated by narrow gaps, a characteristic shared with other Gadiformes.
The ventral side of the fish features two distinct anal fins, positioned beneath the dorsal fins. The pelvic fins are positioned forward on the body, situated beneath the pectoral fins, which is another trait typical of the Gadiformes order. These fins, along with the fish’s overall fusiform or torpedo-like body shape, contribute to its semi-pelagic lifestyle as a schooling fish.
The head possesses large eyes and a lower jaw that protrudes slightly past the upper jaw. A small, often rudimentary barbel can be found on the chin, although in some individuals it may be tiny or effectively absent. The lateral line, a sensory organ, is also noticeable, running from the head toward the tail and dipping slightly mid-body.