INTRODUCTION.
Full-grown fishes have generally some distinct marks by which they can be recognized with certainty. It is not so easy with the young, which often differ greatly from the old ones in shape as well as in color and markings. Their eyes are proportionately larger, their bodies slimmer (see drawing of silvery shiners). Young salmon have black crossbars like yellow perch, etc., etc. Males and females often differ greatly, particularly in the spring.
In examining a young fish, compare the fins with the description in the key. This will lead to a certain group of fishes; and if the specimen is not readily found among them, examine the shape and position of the mouth, the shape of the gill covers, and the size of the scales; find by measurement how many times the length of the head and the depth of the body are contained in the length of the fish; then compare the specimen in these respects with the drawing of the fish most like it in other particulars.
The Latin names of fishes have often been changed. The names here used are taken from Prof. D. S. Jordan's Manual of Vertebrate Animals, 1894.
