Over the years observing steelhead, both hatchery and wild, I've arrived upon a theory that may make some sense. For me, this theory is self discovered, I've never read or heard anyone propose it before, but like most things, someone else may have already written about it. So, that being said, I'm going to offer it up and see if anyone else has observed the same behaviors and/or see if anyone see's any flaws in this theory. First of all, a little background. Like many steelhead fisherman, I started out as a trout fisherman, fishing both spring creeks and freestone rivers around the western states, primarily Utah, Wyoming, Idaho, and Montana. One thing that was/is immediately noticeable is that those fish that are found in spring creeks and/or tailwaters, i.e., water that remains fairly constant in temperature, has minerals/structure conducive to large amounts of insect life, tends to produce trout that are much more selective. This makes sense because with all of the food available, the trout have plenty of time to observe and decide whether or not they are interested in feeding on each object as it floats down the river. In contrast, those trout found in high mountain rivers, and/or rivers where insect life is somewhat scarce, produces trout that are extremely aggressive toward anything that remotely resembles a food source. In some cases, I've watched trout move nearly 10 feet to take a royal wulff as it floated down stream. This aggressive behavior makes sense because food is somewhat few and far between, and a trout that has any ability to survive is going to take advantage of any potential food source. Because these fish are so "non" selective, almost any pattern can be used to great success. Now, with that said, let's again visit steelhead behavior. Hatchery fish, having been raised in a cement tank and given as much food as they desire, tend to develop traits that more closely resemble "spring" creek fish. Their behavior is a learned one, they're able to sit back and wait for their daily feeding routine. As I understand it, most hatchery fish are fed 2-3 times daily. Some fly fisherman who fish hatchery fish will state that there is a noticeable "bite" that take place about 9:00 a.m., then again around 12:00 p.m., and another around 4:00 p.m., the thought being that these are the basic feeding times of hatchery reared fish. Again, in contrast, wild fish are not fed on a schedule, and because our streams (especially coastal streams) do not have much insect/food sources, young steelhead must learn to be aware of anything in their aquatic environment that resembles food, prior to smolting and heading off to the ocean. Their behavior resembles those same trout that are reared in mountain streams. They learn to be aggressive at a very early age, their survival depends upon it. And while there are never any "absolutes" in fishing, what I've observed is that hatchery fish tend to like smaller fly patterns, something from size 6-2. I rarely fish flies larger than that except under poor visibility. Some fly fisherman go as far as to say that hatchery fish won't take a fly. I've found that hatchery fish will usually not move as far to a fly as a wild fish, but they will take them, the fly just has to be nearer to the fish, and I propose that this has is the result of the environment in which the fish was raised. I've also found that hatchery fish tend to prefer sparser flies, when river conditions allow. My observations are that size, color, fly-fullness have to be factored in based upon the weather, water conditions, light conditions, and the time of the run being fished, and whether the fish are hatchery or wild. Fresher fish tend to hit larger patterns than fish that have been in the system longer, as they tend to be a little more gun shy. With wild fish, I'll also fish smaller flies if water conditions will allow, but I'll also fish large flies, flies from size 2-2/0. I've had steelhead smolt attack flies that were roughly 1/3 of their size.