The Stability of the Vitelline Membrane and the Requirements of Developing Trout Ova

Abstract

Rupture of the vitelline membrane by movements of the embryo's tail causes the trout ovum to become permeable to water at about the eyed stage. Mechanical agitation, direct sunlight, and strong, direct electric light may cause the death of trout ova in the pre-eyed stages by injuring the vitelline membrane. After the pre-eyed stages slight agitation, direct sunlight, and strong electric light do not produce apparent harmful effects on ova. A normal electric lighting system may be used in a hatchery without causing harmful effects. Dissolved zinc does not cause the death of an ovum by injuring the vitelline membrane. If the death of a.fertile ovum has been brought about without the vitelline membrane being injured the tissues may disintegrate (particularly in the early stages of development) before the ovum turns white. Subsequent treatment with glacial acetic acid will not then show the stage of development reached at death while in some cases the ovum will appear to have been infertile. The trout ovum contains all substances necessary for development (with the exception of water and oxygen) until the fry begins to feed. Dietary deficiency in trout may result in inferior ova being produced although the parent fish appear to be in excellent condition. Trout ova will develop normally on flannelette kept: damp with distilled water.