Researchers in British Columbia, Canada, noticed 50 years ago that when they rinsed their hands in a stream containing migrating Pacific salmon, those salmon below the wash site suddenly became agitated, broke school, and retreated downstream. A few simple experiments revealed that the odor of human skin was the culprit. Researchers gradually broke down the chemical mixture. Amino acid common in human skin, L-serine, triggered much of the repellency.
Do bass show this same type of alarm reaction to human odor? If so, do bass anglers need to worry about it? The answer is no, all fish are not the same. No evidence presently links bass repulsion with human odor. To the contrary, bass actually find L-serine slightly attractive. Bass anglers who worry about minimizing their body odors while fishing are probably wasting their time, at least from the bass's point of view.
Although human odors may not be repulsive to bass, numerous man-made odors certainly are. By far the worst is the active ingredient of insect repellent known as DEET.
Though specifically made to repel insects, DEET repels just about everything that swims, crawls, flies, walks or runs. Laboratory research at Berkley has shown that bass detect DEET at concentrations of less than one part per million. Fish really, really do not like DEET and bass spew out objects with the chemical in no time flat. Merely touching a lure after a single application of DEET to the hands is enough to contaminate a lure. And the contamination on the hands is long-lasting, enduring at least ninety minutes after the application.
Surfactants, which are better known as detergents or soaps, are offensive to fish. Surfactants act to make oily substances soluble in water. Some are worse than others but when mixed with water they can do considerable damage to a fish's gills.
SDS is perhaps the worst known to date. Although the bass detection threshold for this substance has not been determined, sharks are repelled by SDS at a concentration of just 200 to 800 parts per million. That's potent enough for the Office of Naval Research to consider it as a potential shark repellent for protecting downed pilots.
Other substances bass find offensive are commonly used, including many food and lotion preservatives, especially those derived from benzene. The active ingredient of many sunscreen brands, PABA (p amino benzoic acid), is also repulsive to bass. At least one scientific study has shown minnows to be repelled by nicotine. Caffeine is believed to taste bitter to fish in general.
Some substances that are typically thought of as offenders truly aren't. Neither gas nor oil, for example, is repulsive to bass. We have offered bass food dipped in straight oil, only to watch them eat the coated morsel with no apparent reluctance or side effects.
However, various petroleum additives, such as detergents, can transform oil products making them offensive to fish.