Fish Biology —Eyesight, Smell and Sense of Taste

Ken Jones

Staff member
Fish Biology 101—Eyesight and Smell (From PFIC, 2nd. Ed)

An interesting and relevant fact when it comes to fish and angling concerns fish eyes. Put simply, most fish cannot focus their eyes (due to the shape of the eyes themselves). The result is a fish world in which nearly all fish are nearsighted. Correspondingly, most fish cannot really identify an object until they are fairly close to it. (Even when a fish comes to a lure from a distance they may be reacting more out of curiosity or changes in the water rather than attacking the lure. Of course when they get close to the lure they can see it, and if the angler’s presentation is correct, they may attack it.) However, since water often has poor visibility to begin with, eyesight is not as important to fish as their other senses in locating food (their prey). Instead, most fish tend to use their sense of smell to hone in or track where the food is, use their eyesight to pinpoint the location of the food, and then use their sight together with taste to determine the desirability of the food.

Of course, not all fish rely on smell as much as others just as the eyesight of fish can vary. As a general rule, fish that use sight to locate their food primarily feed during the day. Fish that use smell to locate their food feed primarily at night. Of interest, fish anatomists have found that fish that have two nostrils on each side of their snout have excellent odor perception; those with only one nostril cannot perceive smells as efficiently. So what? Well, species that dwell on the bottom, where light levels are low, tend to have two nostrils and typically feed by smelling out their food. Natural bait would be best for these species and when I say natural bait I mean bait that is in good condition and does not have an off smell to it.

In addition, almost all fish have excellent night, or low-light vision (approximately 6-7 times more sensitive to light than humans). When the ability to seek out food by smell is combined with some ability to see during the hours of darkness it is easy to understand why many fish bite better at night. Croakers, rays and sturgeon are just a few of the fish noted for biting best at night and striped bass fisherman can certainly attest to the fact that nights are often the best time for Mr. Linesides.

Sharks of course are probably the best illustration of night feeders that rely on their osmic senses to locate prey. Studies have shown that in some sharks two-thirds of their brain is used in the mechanics necessary to achieve an exceptional ability to smell. Most sharks and rays also have something called a tapetum lucidum located behind their eyes, a device whose purpose is to reflect light back through the eye, thus allowing the cornea two chances to use available light. However, even with this interesting device (which enhances vision in the dark or murky waters), most, but not all, sharks have very poor eyesight. It isn't needed.

Fish Biology 102—Their Sense of Taste (From PFIC, 2nd. Ed)

If fish use smell to locate their food, they just as decidedly use taste to decide if it acceptable. What is unique, at least compared to humans, is the fact that fish have a variety of taste buds, not only on their tongue or mouth, but also externally on their lips and snout and, in some fish, also on areas like their fins. Some fish (including catfish and many croakers) also have barbels that externally are used to judge the food. What this all means is that many times a fish will reject a bait even before it begins to mouth it. In such a situation, the poor pier fisherman may be sitting there with little or no chance of hooking the fish. Live bait looks, smells, and can taste good to a fish even before it swallows it and the multitude of sensations is one reason why live bait is preferable in many situations. Dead bait may, or may not, look good, smell good, or taste good to the fish. With the exception of some scavengers who don’t seem to care (indeed some fish, i.e., sturgeon, will eat almost anything), fresh bait is almost always preferred as a bait. If frozen, has it been handled correctly (kept frozen) and not allowed to thaw which can allow bacteria to give it an “off” smell?

Again, and this is important for pier rats, many of the species that are prized from piers in California—croakers, sharks, striped bass, etc., are bottom species that like to feed at night, or at least in the early morning and late evening hours, and they typically have the best sense of touch. So, a fifth rule is to always use high quality fresh or frozen bait if you are going to use bait. As for lures, it makes a good argument for adding one of the fish attractants to the lure—both to give it a more natural odor and to mask whatever human odors may be on the lure.