Red-eyed black bass
We often hear all sorts of far-fetched theories about why black bass eyes turn red. However, the reasons are quite simple when studied a little more closely. Red eye in black bass is simply an accumulation of blood in the blood vessels that irrigate a structure behind the retina.
There are two reasons why black bass eyes adapt and turn red: light conditions and territorial disputes. When a black bass lives in tinted water or deep water, the light reaching its eyes is very weak, reducing its visual acuity. To compensate for this, a large quantity of blood is sent to the eyes, charged with oxygen and nutrients, improving vision. This change also occurs when fish are fighting for territory or a breeding partner. Red eyes are a way of proving superiority to competitors, but also, in the case of males, of attracting females.
Fish with red jaws
It is also common for black bass to have a bright red jaw, not only where the teeth are located, but also on the flipper and at the entrance to the oesophagus. This pigmentation may be due to two different factors, which may also coincide.
The first factor is the temperature of the water in which the fish lives, especially when it's relatively deep and the water is cold, in winter for example. The second, and much more frequent, possibility is that the fish feeds on a large number of crayfish. Crayfish moult very frequently, several times a year, but the first moult after winter occurs when the water temperature rises. A large number of crayfish then lose their hard shells and become all soft, making them vulnerable to predators. Black bass love crayfish, but it's easier for them to digest them when they're not as hard as bone and their soft claws can't do any internal damage. A molting crayfish loses its brown/olive color and turns red/orange thanks to the beta-carotene it contains, which makes black-bass jaws red.
Adapting to fishing
The redder a black bass's eyes or jaws, the more information we can glean from them. Red eyes in spring mean the onset of prespawn, a period when fish move closer to the edges and are very aggressive. Red jaws and teeth indicate a period when fish are feeding on crayfish, so it's essential to adapt our lures. Crankbaits, rubber jigs or lipless are very effective lures, and black bass love them if the color is orange-red.
