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In the scales.

When bony fishes first evolved, they labored to carry bony armor that Knights of the Round Table would have envied. That scale-like protection was not metal, but strong layers of bone covered with enamel-like dentine, compounds called vitrodentine, cosmine or ganoine. Why did they need such strong or large scales? Eurypterids, giant ravenous sea scorpions, and other invertebrate predators hunted fishes. Apparently eurypterids were so common and carnivorous that in order for fish to survive among them, they had to have a bony suit of scaled armor.

There are fishes in Florida waters today with a lineage reaching back to those armored ancestors. Sturgeons still carry armor plates--ganoid scales consisting of bone and a crystalline salt outer-cover called ganoine. The gar is another ancient fish. Gar have heavy, interlocking ganoid scales, but a cousin, the bowfin, or mudfish, is nearly as ancient and lacks hard, armored scales. These fish are the ancestors of nearly all the fishes we fish for today, including bass, bluegill, salmon, trout, shad, grouper and marlin.

Even though many sharks have an ancient ancestry, most modern sharks have very small scales, called dermal denticles or placoid scales. Placoid scales are like our teeth in that they are made of dentine. They have little points and ridges that can abrade your skin. The ridges on placoid scales act as spoilers, reducing drag as sharks swim.

The tarpon is another ancient fish that has been around since T-Rex roamed the earth. Tarpon have large scales but they are lighter and more flexible than those of its ancestors. Most fish living today have scales like tarpon.

Mackerel and tuna scales are minute and embedded in their skin to cut down on drag as they are constantly swimming at high speed.

Many fish scales, particularly those of species that live in cooler, temperate waters, show annual growth rings, and counting these rings can give the age of the fish. This is not so true of tropical fish. Ear stones, otoliths, are still best for aging those species.

You can see that when it comes to fish, a whole lot of history hangs in the balance of the scales.

By R. Grant Gilmore, Ph.D.
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Title Annotation:The SPORTSMAN'S BIOLOGIST; history of the body armor of fishes
Author:Gilmore, R. Grant
Publication:Florida Sportsman
Geographic Code:1U5FL
Date:Apr 1, 2009
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