The Mechanism of Hardening of the Salmonid Egg Membrane after Fertilization or Spontaneous Activation

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Abstract
The embryonic development of fishes proceeds under the protection of rigid egg membranes which preserve the embryo from mechanical injury. Salmonid fishes bury their eggs in sandy and stony ground so that they are particularly liable to mechanical damage. This is apparently the reason why the membrane of the salmonid embryo is extremely strong, resisting a load of 3–4 kg. per ovum (Gray, 1932; Hayes, 1942,1949; Hayes & Armstrong, 1942; Zotin, 1953a). This mechanical property of the membrane does not appear immediately after fertilization or activation but is preceded by a whole set of processes which are elicited in the membrane by external factors and by the fertilized or activated egg itself. Thus, according to Manery, Fisher, & Moore (1947), hardening of the egg membranes in the speckled trout sets in 2 hours after the release of the egg into water. Ca ions have been shown to be of great significance for membrane-hardening in Salvelinus fontinalis (Manery, Fisher, & Moore, 1947; Warren, Fisher, & Manery, 1947; cf. also Hoar, 1957) and Oncorhynchus keta (Kusa, 1949 a, b). In distilled water, membrane-hardening is slower than in ordinary water and is completely blocked when Ca ions are bound by 0·01 N sodium citrate or 0·02 N sodium oxalate.
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