Understanding a Bass' Sense of Smell
Among fish in general their keenest sense is the sense of smell. Some fish make much use of their sense of smell while others do not.
A catfish feeds with its sense of smell. Salmon avoid sea lions and otters with their sense of smell, and they use an acute sense of smell to return to their breeding grounds. Other fish make little use of their sense of smell.
A bass has two nostrils, one on each side of its snout and water is filtered through these nostrils and over odor sensing nerve endings. Once an odor has been detected a bass can use its stereo equipped nostrils to zero in on its source, much as it can use lateral lines to zero in on an object making a sound.
Like sounds, some odors attract bass and some odors repel. As a fisherman, you need to know which is which.
Gas and oil presents an odor that repel bass and it is easy to contaminate a jig and pig or a plastic worm with gas or oil on the floor of a boat or on your hands.
If you have been handling something (such as sunscreen) that might impart a strange odor to your bait you should wash your hands before continuing to fish. Experienced fishermen carry a small bar of soap in their tackle box for just this purpose. An injured bass puts out an odor that alarms other bass. Thankfully, being hooked in the mouth does not trigger this odors but an injury to the gills most assuredly does.
Therefore, it is appropriate to release a bass that was previously hooked in the mouth, but it is best that you keep injured bass in your boat until you are ready to leave the area.
Baitfish all have odors that attract bass, and a wounded baitfish puts off an odor that is particularly attractive.
For this reason people fishing with live minnows are well advised to clip the minnow slightly with a nail clipper. Some accept the effectiveness of adding fish attractant to worms, jigs and pigs, grubs, and the likes.
Fish are attracted to the bait through smell as well as sound and appearance. Smell helps induce a strike, and it causes fish to hold onto the bait longer.
The down side, of course, is the slimy stuff messes up your hands, the boat, makes knots harder to tie, and is generally a pain in the butt.
It is a trade off, but most serious bass fishermen routinely use fish attractants.