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Growth Rates of Brook Trout Reared upon Purified Rations, upon Dry Skim Milk Diets, and upon Feed Combinations of Cereal Grains^*

From the Animal Nutrition Laboratory, Cornell University and Connecticut State Hatchery, Burlington, Conn.

Experiments attempting to define the fundamental nutritional requirements of the lower vertebrates have been continued with brook trout. Experimental groups have been stunted for periods exceeding twenty weeks by feeding purified rations containing a low level of protein and by feeding a limited amount of a protein food, as raw liver. In both cases trout will exhibit an optimum growth after long stunting when they are placed upon an adequate diet. Alternate periods of stunting and growing indicate that there is a tendency toward compensation during the growing period which makes the rate tend to exceed the normal optimum.

The factor in raw meat which seems to be the most active agent in stimulating the growth of trout is not extracted by alcohol nor ether. It is not identical with any of the known vitamins.

Synthetic purified rations of starch, casein, and salt mixture with vitamin supplements will permit a limited growth in trout if the protein level exceeds ten per cent. Trout are equally stunted when the protein level is ten per cent whether the ration contains three or six per cent mineral matter. Trout stunted upon low protein diets live twice as long as those that are allowed to grow upon similar synthetic rations with a higher protein level. This seems to indicate that their bodies contain a store of some substance that is essential for life but is consumed in growth.

Dry skim milk has been studied as a trout feed. Experiments with various traces of mineral supplements indicate that its failure is not due to deficiencies in zinc, copper, iron, or iodine. Raw liver is a much more effective supplement for a milk diet than raw spleen. Dried buttermilk is slightly better as a trout feed than dry skim milk when each is employed singly.

Trout are able to use corn gluten, flour, and peanut meal for growth and maintenance. As a converter of matter, the trout compares very favorably with the most efficient of the higher mammals and is possibly somewhat superior.

Manuscript received 20 November 1928.