A quantitative study of the total fat content of developing salmon eggs

Abstract

An investigation into the problem of foodstuff metabolism involves chemical studies of the embryo and the supply of food at various stages of development. Naturally those eggs which are easy to rear and which contain large food stores in the form of yolk provide the most convenient material for an approach to the problem. Knowing what foods the egg contains at the beginning of development, the absorption processes can be studied by separate analyses of embryo and yolk throughout development. By this method, Needham (1927a, b) and other workers have been able to follow the protein, fat, and carbohydrate metabolism of the chick from the third day to the end of incubation. The results indicate a succession of energy sources in the order: carbohydrate, protein, fat. This phenomenon is probably of wide significance, but generalizations upon the matter are unsafe until it is known whether or not a similar situation exists in other embryos. The salmon was chosen because its eggs are larger than those of other common teleosts and can be maintained in the laboratory with very little attention. It seemed reasonable to expect that if there were fundamental laws governing the fat metabolism of vertebrate embryos these would be disclosed by the comparison of members of two such widely separated groups as the birds and the bony fishes. In planning the investigation it was desirable to secure data similar to those already existing for the chick in the hope that direct comparisons might be .facilitated. For this reason we have estimated throughout development: (1) the total fat content of the embryonic system (embryos plus yolk); (2) the total fat content of the yolks only; (3) the total fat content of the embryos only; (4) the weights of separated embryos.