RAINBOW TROUT, a freshwater fish (Sohn° irrideus) indigenous to the mountain streams and rivers of the Pacific Coast of the United States, but widely introduced into Eastern waters. From the eastern brook-trout (Salvelinus fontitutiis) it may be easily dis tinguished by its colors and the presence of teeth on the vomer bone; from the related sal mon trouts, with some difficulty, by its small mouth, and the number of scales, about 135 in typical examples, along the lateral line. The rainbow trout is exceedingly variable and many distinct forms, which are considered by ichthyol ogists to be modifications of this species but which have received distinct vernacular names.
are found particular streams or watersheds. The complex relations of the various species of trout and salmon to their environment is little understood. From fish culturists the McCloud River trout (S. irrideus shasta) has received much attention since 1880. This variety is particularly well adapted for stocking streams and ponds in which the brook,. trout no longer thrives, owing to the clearing of the forests and the resulting higher tempera ture and increased muddiness of the water. To supply the great and constant demand for young fish for stocking purposes the Federal Fish Commission maintains several large hatch eries and many States, others. Carefully selected
breeding fish are kept in specially constructed ponds designed with reference to cleanliness, good circulation and ease of handling the fish. Spawning occurs during the winter. The ripe females are stripped in the usual way and the eggs mixed with the milt in a pan either with or without water. After a few minutes water is added and they are gently agitated and re peatedly washed to remove the surplus sperm, and, after standing about an hour, are trans ferred to the hatching trays, which are con structed of galvanized wire, These trays are arranged in troughs with running water in such a way that the young fry fall into the latter as they hatch. As the fry grow and begin to feed they are distributed to other troughs and finally to rearing ponds, constructed in a manner to insure cleanliness and an abundance of flowing water. The young are fed on ground liver and are transplanted when several months old. They grow rapidly, but in the East never attain the large size which they do in their native streams. They feed on insect larvae, etc., and may be fed artificially on chopped beef or liver mixed with corn meal. For angling purposes the rainbow is inferior to the brook-trout, but is a fair sub stitute.