Jim explained that they are interested in large steelhead over 20 pounds, as they have tons of samples of the smaller variety. These larger fish, including salmon, are older and therefore have more information to provide to the analyst. What Jim could tell me about our fish was that both the 22+ and the 23.5 pounder were 6 year old bucks that had spent 1 year in fresh water, 5 years in salt water and had no repeat spawn. I wondered how he came to these conclusions.

The first step in the process is to obtain a proper scale sample. The proper area to obtain a sample is at the rear end of the dorsal fin above the lateral line. The reasoning behind this is that fish lose scales during their lifetime. When a scale is lost a new one grows back without any of the previous years growth rings. The biologist needs scales that have been on the fish from the beginning. The area posterior to the dorsal fin is the least venerable to scale loss, therefore the scales are most likely to be fully mature. Especially with steelhead, a large sample is preferred to insure that a readable scale is included. These scales should be placed in a proper envelope which anglers can carry at all times in their vests or tackle boxes. The hatchery and Fish and Game distribute these envelopes for Jim. He uses small manila coin envelopes which he stamps with places to fill in date, where caught, length, girth, weight, sex, etc. The more information provided the better. These scales should not be placed in plastic bags as bacteria can destroy their value. Dry is the key. Some of these dried scales are still usable 20+ years later.

Coho age 3
(Three years old, having left freshwater in its second year)

Most fish are born without scales, but the young fish starts to form scales when it is about 4 to 5 centimeters long. As the fish grows, the scales increase in size while the number of scales remains the same. The portion of the scale that is imbedded in the skin is called the anterior, because it is toward the front of the fish. The exposed part is the posterior, since it is closer to the tail. The bony rings (annuli) are only in the anterior portion. The margin between the anterior and posterior is often used for reading the annuli. The first scale remains at the center of the growing scale as long as the fish lives and is called the focus. Fine ridges called circuli are laid down in a circular pattern around the focus like the growth rings of a tree. Growth in fish is not continuous over the entire year. The circuli are widely spaced in warm seasons when growth is rapid and closely spaced in cold seasons when growth is slow. One year's growth is revealed as a series of widely spaced spring and summer circuli followed by a series of closely spaced fall and winter circuli. The outer edge of a series of closely spaced circuli, called an annulus, represents the end of growth for that year. Rings formed in fresh water are usually finer than those added in salt water. Food is more abundant in the ocean than in streams, so the fish generally grow faster, but even in the ocean, food sources may vary, and fish will grow at different rates.

Most fish have two main types of scales. The cycloid scale has a smooth exposed surface and is commonly found on the salmonids. The ctenoid scale has a minutely indented surface which is rough to the touch and is found in the warm-water game fish (i.e. sun perch). Other hard parts of fishes show similar increments of growth and can be used for age determination. Sections of vertebrae bones of otoliths (ear stones) can be used.

Jim enlarges these scales on a microfiche machine so he can read them. I have included some samples of scales here so you can see what he sees.

Once again there is an opportunity for the fisherman to provide an invaluable service to his hatchery and stream population. Scale sampling can be added to catch-and-release, habitat restoration, and hatchery involvement, as another means for us to give renewed life to our resources.

Columnist Joan Carter co-owns, with her husband, Dan Carter's Guide Service.