It has long been known that ripe males occur among salmon parr, i.e. in young individuals, up to 15 cm. long, which have never left their native river. One of us (G. M. K.) has seen them frequently during the last 28 years on the Wye, Towy and Dee. These males have mostly been regarded as occasional precocious males (Calderwood 1930), and there has been no recognition that the male phase may be normal and functional in the fresh water life of salmon before they migrate to the sea. Recently knowledge of these so-called precocious males came to one of us, and in view of the peculiar biology of the salmon it was thought that a male phase might be universal and normal in salmon parr (Orton 1937) and an investigation of the problem was begun. Literature A century ago Shaw (1840) in a paper proving that parr were the fry of salmon also noticed that male parr with ripe milt accompanied adult female spawning salmon. He concluded that the young males might be fertilizing the eggs, and showed by an experiment with milt from a young male parr and ova from an adult salmon that successful fertilizations could be made, and that the progeny became parr like the male parent. Unfertilized controls in a stream of pure water gave no fry. Further, he reared the progeny of this cross and from one young ripe male again fertilized successfully ova from an adult female salmon.
Precocious males of cultured Atlantic Salmo salar L. in the second spawning season