s are transparent microscopic animals which live in fresh or salt water. They abound in the surface waters of great lakes, and swarm through the shal… - Ann Haven Morgan

As the spawning season approaches, fishes move toward the shores of ponds and lakes or upstream in the creeks. Some of them, such as perch and sunfish, only swim in among nearby weeds or protecting stones. The journeys vary from such short ones to the famous migrations of river salmon, extending over hundreds of miles; but they all end at spawning grounds or nesting sites. During this time color differences between male and female appear or become more marked.

... s feed upon microorganism from the muck and water of the bottom and in turn are consumed by es, s and mankind.

... The two problems which face every organism are those of maintaining its own life and continuing its race. Its youth is devoted entirely to satisfying its individual needs for food and safety; its adult life is devoted to the race, but the necessities of the individual are still satisfied though they may be secured in an entirely different way. The immature life of is aquatic, and to it all adjustments concerned with food or safety are exclusively confined. The mature or adult life is aerial. It is solely devoted to reproduction. There is no provision for food or for other means of lengthening its life. It gives an opportunity for studying ways of getting a living which have been completely isolated from ways of reproducing.