While I am convinced of the truth that the insect diet of game-fishes induces a faster growth and more gamy qualities, it is out of the question for nature to supply even a small part of the insects that are necessary to sustain a fair number of fish in any water. Even if we include bottom creepers, vast in numbers as they are, all would not suffice to supply the food required to make trout lusty and plentiful. In the temperate zone, aquatic insects do not rise over the water in any great quantity till after the first week in May. From that time on, they rapidly develop, if weather conditions are at all favorable, till the apex of their abundance is about the first week in June, when over two hundred species of insects change from the creeper state at the bed of the river or lake to rise above the surface for one to three days, solely to perpetuate their species and then die. During that period all the trout family feed and gorge, night and day, taking on flesh and sleekness to a greater extent than at any other part of the year. No matter whether you capture trout at early morn or late at eve, their stomachs are crammed full of undigested insects.
As long as insects rise, so long do trout feed. From June the fourteenth the vast number of insects rapidly declines, until at midsummer and during the hot season, aquatic insects are rarely seen during the daytime, and trout are then almost impossible to capture with artificial flies. Many anglers are puzzled at this curious condition. Just the very time the fisherman wants his vacation and goes fishing, he is confronted with the annoying fact that trout are sluggishly inclined to his flies during the daytime. His only chance of success is while trout are visibly feeding for a short time between sunset and dark. The puzzled and vexed angler may be interested to know that aquatic insects are extremely sensitive to both heat and cold. They won't and don't rise on a cold day, nor do they on a hot day. They patiently wait on hot days to rise over the water in the cool shade of evening and night.
The question arises, What are trout doing on hot, sultry days? The answer is simply, they are doing nothing except lying still, poised at the bottom, where the water is coolest. With stomachs jammed full taken in during the previous night, they can be patient and await their evening meal. Another question might be asked, If no insects abound on sultry days, why don't trout rise to the angler's perfect imitation, played dry-fly fashion, just as the natural insect floats along the surface? Sometimes they do, but most often they don't. Very often they swim up just to say, "No, thank you." Trout are very cunning and wary, especially old ones. There is no doubt whatever that trout prefer insects to minnows or other food-fish. Whether it is because insects are easier to capture or more palatable, the fact remains that artificial flies are the best lure for trout during the heavy rise of insects in late May and June. I have never found a mixture of flies and minnows in their stomachs at that period. It is either one thing or the other. Before insects are very abundant, the stomach contents are most often bottom creepers; now and then may be found a minnow, or at early season flood times we find various worms.
Scientists have made tests on the rate of growth of aquarium specimens on different diets for trout. The result is interesting and quite natural. Trout grow four times as fast on insect and creeper diet as they do on fish diet. Fish food is twice as effective as a diet of worms. When insects become scarce, from the end of June to the end of August, trout turn their attention to a diet of fish, grasshoppers, crickets, caterpillars, and the creepers which are about to emerge for the late autumn flight when the temperature is more normal. We find in September and October insects again become abundant, though not so thick as the spring rise, but sufficient to attract trout, and induce them to feed on insects exclusively till severe cold sets in. Therefore it is apparent that minnow baits, live or artificial, are most effective and best to use, all through the season except the insect glut late in May and early in June. These conditions refer more especially to waters of the Eastern seaboard of the temperate zone, from the Delaware to the St. Lawrence, including Maine, though the latter may be said to be rather later than the waters of the higher Catskills and Adiron-dacks.
Trout naturally grow to a greater size in the deep, cool lakes than in fast-running streams, as less effort is required to get food, which is nearly always abundant because of a greater range for fish food to breed. The most fastidious epicure cannot detect any difference in the taste of a cooked trout taken from lake or stream, if both fish have subsisted on similar diet in both situations - if it be in the wild state. The case is entirely different with trout reared by artificial means and fed most often on chopped liver and eggs. The effect of the artificial rearing and the food consumed, is fully apparent in the taste of the fish when cooked. In addition to that, artificial food has a deterrent effect on the gamy qualities of trout, making them dull, listless after being hooked, no matter what bait is used to capture them.
The real truth is, the more fish have to hunt for their food the more gamy do they act on the restraining line. There is also no question that those trout captured by means of artificial flies, while feeding on insects, are always more strenuous in resistance, in other words more gamy, than if captured on any other lure while taking other food. It is also the greater activity required in getting their food in the swifter waters that makes trout and bass more gamy in resistance, and their activity is more prolonged. In such waters they become more adroit and skilful in ejecting the hook, at the same time in such situations they are more bold and aggressive, taking the bait or fly at top speed, just as they doubtless do for their natural food. I have witnessed trout dart upward to my minnow or fly, miss it, then turning down-stream, rushing along after it like a flash, taking the lure with a smash most admirable to behold. No need of a strike of the wrist, no fear of their being unhooked; they take the lure as if it were their natural food, without fear or scruple.