What makes a fish go for your fly is a topic highlighted in an article by Dr. David Ross, a senior scientist with Woods Hole Oceanographic Institution in Hyannis, Massachusetts. In previous articles for Saltwater Fly Fisherman, Dr. Ross has discussed the senses that are most important to fish: smell, hearing and vision. In the April/May 1999 issue of Saltwater Fly Fisherman, Dr. Ross talks about whether or not your fly is appealing. This is a really terrific article and one worth reading. Here are some highlights.

Basically, the senses of taste and touch don't factor into a fish's initial attraction to a fly. Rather, to react to your fly, a fish must smell, hear or see it. When you hook up, a fish has made one of these three sensory responses.

Most fish, especially game fish have an excellent sense of smell; some fish species detect scent a million times better than humans do. A fish's sense of smell can be particularly useful when the water is dark or too turbid for its vision to be effective. Some species of fish communicate via scents; some fish actually emit chemical odors to attract members of the opposite sex for mating, or to indicate danger or food.

Anglers, particularly those, who fish offshore, often capitalize on a fish's excellent sense of smell by putting out chum to entice feeding activity. Fly fishers also use this technique by free drifting chum flies (flies that resemble pieces of bait) into the scent trail, a technique that's effective for most offshore marine species. Some anglers even go to the extent of putting fish oil on their flies. But this would disqualify anyone from an IGFA world record. Actually the most effective substance is human saliva, which is why some fisherman feel that spitting on their flies will improve their luck.

Fish are very sensitive to sound. How many times have you been in the flats when someone in another boat slammed down a hatch? You can visually see fish life exploding underwater (called blowouts) as fish react to the sound generated. Fish detect sounds in one of two ways: using their inner ear, or using their lateral line. Fish can register sounds on their lateral lines within a range of 20 to 30 feet (what scientists call the near field). Noises within 5 feet or less are picked up with extreme accuracy. Sometimes fish make vibrations by swimming and then use the sound rebounding to their lateral lines to detect nearby object possibly even flies.

Fish not only detect near-field sounds with their inner ears, but also sounds coming from far away (from the far field). Species that have an inner ear attached or close to their swim bladders typically have very sensitive hearing, because the swim bladder acts as a sound-amplifying organ.

Because fish are so sound sensitive, it makes sense that noise-making flies are often effective. Some noisy flies contain rattles (Rattle Rouse), others cause a surface disturbance (Ultra Hair Bug), and some are bulky and push water (Tabory Snake Fly). Rattles and poppers may draw fish from far distances, while flies that push water work better in the near field. Noise making patterns are probably less effective in the surf zone. Keep in mind that fish are wary of any unfamiliar noise, such as boats, wading, or a fly slapping the water.

Dr. Ross believes that vision is of less value to fish for their survival than smell or hearing. However, it's not known what fish actually see. There is evidence that some fish may see in a special range beyond what humans see, including seeing in polarized light. Most offshore gamefish only have blue and green in their spectrum. So distinguishing colors are less important. Some recent research by Australian scientists indicates that Marlin may detect some colors when the fish hook up closer to the surface.

One important factor to consider - are the fish hungry? Some fish will gorge themselves and others will not eat at all. During full moon periods, fish will eat at night and just lounge around during the day. You know how frustrating it is try to fish after a full moon.

Also tides and weather influence feeding. So fly pattern, color, shape, and motion won't make much difference. Another factor is how similar in size and shape is your fly to the baitfish being consumed. Some anglers feel the size and shape of the fly is more important than color. I believe bigger flies catch bigger fish.