When you aren't feeling well, first thing the doctor does is to take your temperature. When fishing isn't too good during hot weather, it can be a good idea to take the temperature of the first fish you catch from a lake, too.

Crazy idea? Not at all. Doing so tells you exactly the temperature of the lake depth from which that fish came. Then, by using an underwater thermometer and finding that same temperature zone, you have some hot information on the location of similar species of fish.

Being cold-blooded creatures, fish tend to take on the same temperature as the water. In summertime, all deeper lakes divide into three "layers." The top level is warm, while the lower layer is coldest but may lack enough oxygen. It is the center section in which most fish prefer to stay if they like cool water; if not, they will be in the upper level.

Most fish, when feeding, tend to venture in and out of their comfort zone. This might be why you catch a trout or smallmouth bass in water you know is too warm for them; the fish just made a quick trip away from its preferred temperature layer, intending to return there after grabbing your lure, which it mistook for food.

To be of help to you, a fish's body temperature must be taken within a minute of the catch. This is done with a special thermometer sold by better sporting goods stores (or it can be ordered from Orvis). Other electronic devices on the market will also work for this purpose. Depth thermometers, of course, are easier to find, although a surprising number of anglers don't seem to even know about them.

Preferred temperatures are not likely to vary more than five or six degrees, although there are always exceptions. For example, largemouth bass like 80 to 86 degrees, while smallmouths prefer something around 70 degrees. Given the choice, walleyes haunt 73-degree water, while a muskellunge likes his temperature around 75 degrees. Bluegills want something between 80 to 85 degrees, while yellow perch prefer 68 degrees.

Lake trout like 44 to 53 degree water; rainbows, 50 to 65 degrees; brook trout, 48 to 64 degrees; and brown trout, 55 to 65 degrees. With salmon, both chinook and cohos seem to prefer temperatures in the 44 to 58 degree range. If trying to locate whitefish, try 44 to 63 degree water.

The most active feeding temperature will be toward the middle of the ranges given here, although the lower edge will likely produce the best results for you. Afish that is too warm or too cold, however, seldom feeds with much enthusiasm, if at all.

For this reason, it can help your success rate considerably if you have a pretty good idea of how cold the water is under the surface. If temperatures are uncomfortably warm on bottom, the fish will head for deeper water to find a better comfort zone. Your bait should follow them there for best results.

Editor's Note: Gordon Charles, who died May 2 at the age of 86, had provided The St. Ignace News with four of his "Outdoors With Gordie" columns to use throughout the month. Mr. Charles was a contributor for many years to this newspaper and several other northern Michigan publications.