Four ingredients of a dry diet, Santa Monica, and a special food supplement, were tested for their effects on the occurrence of hepatomas in Salmo gairdnerii. When cottonseed meal was omitted from the diet, no hepatomas developed in the experimental fish. When the same diet with its usual cottonseed meal component was fed, 48 percent of the fish developed hepatomas.

No abstract

Whirling disease of trout, caused by Myxosoma cerebralis, was diagnosed in 1966 for the first time in rainbow trout (Salmo gairdneri) from California and Nevada hatcheries. In 1969 the first incidence of this disease in cutthroat trout (S. clarki) was reported in Nevada. To date these have been the only confirmed cases of whirling disease in western United States.

GAME, in an effort to Eeep the cost and availability of its trout hatchery foods In balance with its expanding catchable-trout program, has resorted in part to the use of pellet diets.The pellets are composed of various antreal and vegetable meals and are manufactured to the State's formula by a co•nercial milling company.The method of introduction of the pellets to the trout has posed a problem. During the early .par• of their lives, the fish are fed on meat diets; and when pellets are introduced, a tr•lnt•g period is usually required.It has been noticed that fish in warm-water hatcheries (hatcheries with water temperatures above 54 ø F.) will accept pellets sooner than fish in cold-water hatcheries. Considerable waste occurs at some hatcheries even after the fish have become used to feeding on pellets. This is mainly due to the reluctance of the fish to pick up pellets which have fallen to the pond bottom. This last problem may be somewhat eltm2uated by slow and careful feeding, but in large production hatcheries such feeding is virtually impossible because of the time element. At the suggestion of M•. Lee Talbott,Assistant Supervisor of Fish Hatcheries, various food dyes were used to color pellets in the hope that some color might make them more appealing to the fish. Pellets were colored green, blue, yellow, and red. These colored pellets, together with some standard pellets (which are a light tan in color), were then fed to some catchable-sized rainbow trout ( Salmo gairdnerii). The fish reacted to the green, blue, and yellow pellets as they did to the standard, or uncolored, pellets: the fish ate some but allowed many to fall to the pond bottom, where they were then i•nored. W•en the red pellets were fed, the fish reacted in the same vigorous manner as when they were fed meat. Con-tinued observations revealed that rainbow trout which had never been fed on pellets showed a vigorous reaction to the red pellets but tended to ignore the other variously colored pellets.Further tests showed that red pellets were picXed off the bottom, while the green, blue, and yellow pellets were not. It was felt from these demonstrations that it would be worthwhile for us to color our pellets red, thereby almost ell m• uating the training period and also reducing the amount of wastage. It was found that we could color lO0 pounds of pellets in a concrete mixer in about 5 minutes. This was done by adding t ounce (about 12 cents' worth) of F.D.&C. Amaranth No. 2 •Ood and D• Administration' s specification_• red dye (powder form) and it •llons of water to the pellets in the mixer. Since our concrete mixer would hold only about 25 pounds of pellets, we reduced the amount of dye and water proportionately.The dye was dissolved in the water and added to the mixing chamber of the concrete mixer, which contained the pellets.The mixer was then started and operated at a slow speed with the mixing chamber in such a position that the pellets fell at the top of the ride, thus insuring a good mix. In about 30 seconds the pellets were well colo...

Four ingredients of a dry diet, Santa Monica, and a special food supplement, were tested for their effects on the occurrence of hepatomas in Salmo gairdnerii . When cottonseed meal was omitted from the diet, no hepatomas developed in the experimental fish. When the same diet with its usual cottonseed meal component was fed, 48 percent of the fish developed hepatomas.