Micropterus dolomieu, commonly known as the Smallmouth Bass, is a highly sought-after freshwater game fish in North America. Smallmouth Bass do have red eyes, though the color is often more subtle than bright crimson. The eye coloration is a distinguishing feature, frequently appearing as a deep amber, reddish-brown, or orange hue, which sets it apart from many of its relatives in the black bass family. This striking trait is a result of specific biological mechanisms and can vary greatly depending on the individual fish and its environment.
The Specifics of Smallmouth Eye Pigmentation
The characteristic reddish or amber coloration of the Smallmouth Bass eye is due to specialized pigment cells called chromatophores located within the iris. The color is primarily attributed to the presence of xanthophores, which are cells containing yellow and red-orange pigments known as carotenoids and pteridines. These pigments combine to create the fiery, bronze-colored iris that is a hallmark of the species.
The pigmentation is not typically a brilliant, fire-engine red, but rather a deep, metallic amber-red or reddish-brown hue. The arrangement and density of these xanthophores, along with darker melanophores, determine the exact shade of red or orange observed in any given Smallmouth Bass.
Factors Influencing Eye Color Variation
The intensity and exact shade of the reddish eye are not uniform across all Smallmouth Bass populations and change based on environmental and physiological factors. Water clarity is a significant influence. Fish inhabiting clear, cool waters often display more vibrant and distinct red or amber eyes. Conversely, Smallmouth Bass living in stained, murky, or darker river systems may exhibit a duller, more brownish or bronze eye color.
Diet also plays an important role in the vibrancy of the eye and body colors. The carotenoid pigments responsible for the red and orange tones in the iris must be acquired through the fish’s diet. Smallmouth Bass that consume carotenoid-rich prey, such as crayfish, often exhibit a richer, deeper orange or red coloration. Additionally, younger bass may display less pronounced coloration, while mature fish, especially males during the spawning season, can show a temporary increase in color intensity.
Using Eye Color for Species Identification
The reddish-amber eye serves as a practical, preliminary identifier when distinguishing the Smallmouth Bass from its most common relatives, the Largemouth Bass (Micropterus salmoides) and the Spotted Bass (Micropterus punctulatus). The eye of the Smallmouth Bass is reliably reddish or bronze-tinged, a feature that is typically absent in the other two species. Largemouth Bass usually possess a dark, often black or gold-rimmed eye, while Spotted Bass eyes are generally dark or gold, lacking the distinct reddish hue.
Eye color alone is not a definitive identifier and must be used in conjunction with other distinct physical characteristics. The Smallmouth Bass has a jaw that extends only to the middle of its eye, whereas the jaw of a Largemouth Bass extends noticeably past the rear edge of the eye. Smallmouth Bass also feature faint, dark, vertical bars or stripes on their sides, instead of the prominent, continuous dark horizontal band seen on a Largemouth Bass. The Spotted Bass, while also having a jaw that does not extend past the eye like the Smallmouth, can be identified by the rows of dark spots along its lower side.