Animal rights groups attack catch-and-release fishing, believing the pain system in fish is the same as in birds and mammals. Zoologist Austin Williams claims that “fish are sentient organisms, so of course they feel pain.” Fish experience fear, he says, and react with increased heart and breathing rates.

Others insist angling doesn't hurt fish because of the fundamental difference in the nervous systems between higher and lower vertebrates. For example, a fish will return to the same fly, time after time, to be hooked and released many times within a short interval. Contrast this with the behavior of higher animals, wherein avoidance of a painful stimulus can be learned in a single experience.

Dr. Hilary W. Thompson, professor of ophthalmology, biometry, and neuroscience, relates his account of fishing for largemouth bass in south Florida. The fish was clearly visible in shallow water. “I threw a yellow rabbit strip leech at him and he clobbered it immediately,” Dr. Thompson said. “Released, he swam quickly back to his station, and I threw at him again. Once again he took the fly and when released, took up the same stand.” On the fourth catch the bass was moving more slowly, so Dr. Thompson terminated his experiment. “As far as I could tell, he took with as much energy the fourth time as the first.” That hook hurt, no doubt—all animals try to escape from painful stimuli once perceived and struggle for freedom. “But the little bass never suffered an anticipation of the pain as a human would.”

As soon as the pain stops, fish resume the business of feeding and schooling or nesting or ignoring flies or whatever fish work they were engaged in. Says Dr. Thompson: “Their brains are not wired up like ours and don't even have all the same parts that our brains do.”

Therefore, the argument that catch-and-release fishing is unethical because it causes fish to suffer as humans do seems illogical.

However, though angling may not hurt fish, many anglers leave behind them a trail of tackle victims. Birds, turtles, and other animals suffer debilitating injuries after swallowing fish hooks or becoming entangled in fishing line. Officials with the Virginia Marine Science Museum Stranding Team say fishing line is one of the top three threats to aquatic animals.