Fishes spawn but once each year, and the time and length of the spawning season is not the same for all species. With some species the season is short, while with others it may extend through three or more months. In the latter case those produced the first part of the spawning season are at the end of six months much larger than those which appear at the close. It is therefore evident that the fishes of any single brood by end of the year will vary greatly in size, often to such an extent that the broods of one season cannot be separated from those of the preceding season; especially is this true of our smaller species. Mr. Moenkhaus, in making a study of the two species of darters, the Sand Darter or "Johnny," and the Log Perch, found by collecting a large, miscellaneous lot of these fishes, from a given locality, that it was possible to separate them in groups according to size of one, two or three years of age, which indicates a quite uniform rate of growth for these two species.

Mr. Voris collected a miscellaneous lot of over five hundred specimens of the Blunt-nosed Minnow from Turkey Lake in Indiana, varying from one to three inches in length. These, when separated as far as possible, according to sizes, did not fall into distinct groups of different ages. In my own collecting and study of fresh water fishes I have always been impressed with the difficulty of recognizing the age of fishes, except that the smallest taken was considered to be the product of the preceding spawning season. Here is an interesting question to which but little attention has been given. Any one will find much interest in studying the rate of growth of fishes under different circumstances. We know that the rate of growth is in no way uniform, as is the case with our warm-blooded animals. We also know that among fishes there is no uniform adult size, as there is in case of warm-blooded animals (birds and mammals). In general, we cannot speak of a fish as being full grown; at the same time there seems to be a limit of size for each species in each body of water, beyond which only a few go. The Chinook salmon we mentioned reach an average weight of twenty to thirty pounds, although individuals are occasionally taken of forty, sixty or even one hundred pounds weight. These large fishes are by no means common, the other species of salmon never attain the size of the Chinook.

There is an interesting family of fishes in our fresh waters known as Minnows; these fishes are too small and too full of bones to become a favorite for the table. They are the most helpless of all our fresh water fishes, being soft, and, as they are slow swimmers, they become an easy prey to larger fishes, and form a large part of their food supply. They have been constantly driven into smaller streams and shallow water, until they have become exceedingly dwarfed. Their only use in the economy of fish life seems to be to assimilate small organisms, converting them into such shape that they can be taken by the larger fishes. Now the Minnows of all the United States east of the Rockies are small and, except in case of a few species, they are less than six inches in length. The predatory fishes, such as the Sunfishes and Perches, Pike and Pickerel, are their worst enemies. In the Rocky Mountains there are none of these fishes, and many minnows there grow to a length of two feet or more. The only enemy of importance they have is the trout, but the minnow finds a more congenial climate in the larger bodies of water, too warm for the trout. The struggle for existence has been a severe one, especially so in Our streams where species of fish are the more numerous. It has greatly limited the growth of most species beyond an average size, and is in many places responsible for the fact that often a species may become dwarfed in certain bodies of water. In the Salmon river in Idaho it was not an uncommon thing to catch trout of three or four pounds weight. In the smaller tributaries and in the smaller mountain lakes it was unusual to catch one weighing over one half pound, the average being less than one-fourth pound. I have no doubt that many of those from the small lakes of one-half pound were as old as the large ones taken from the Salmon river.

Fish eat and grow very irregularly. The average size of individuals, which we would ordinarily call adults, for some species, is different in different bodies of water. Their growth is influenced largely by the size and depth of the body of water in which they live, also by its temperature and the amount of suitable food it contains. The value or extent of each of these influences is imperfectly understood.

The forms of fishes are very numerous. Some are extremely long and slender, as many of the species of Eels, Pipe-fishes and the like, while others are extremely short, like Sunfish of the ocean. Others, like the Trunk Fishes, are nearly equal in all dimensions.