Sur l'introduction des Salmonidés exotiques en France

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Summary

Continuing my survey of attempts to introduce non-indigenous fish into France, I have obtained much information about two Salmonidae species of American origin, with great numbers of the young of which many French waters have been stocked during the last 70 years: Salvelinus fontinalis Mitchill., the Speckled Trout, and Salmo irideus Gibb., the Rainbow Trout.

1.	Salvelinus fontinalis cannot be considered as established in open waters; tests initiated in upper Seine (1907–1908), recent ones carried out in Lorraine, in Rupt-de-Mad tributaries, in the Alps, and in the Vosges, have been negative. No reproduction has been observed, except perhaps in the small stream of the Rive, a tributary of the Romanche (Isère). On the other hand, Salvelinus fontinalis is established in closed waters where generally Salmo trutta L., the Brown Trout, is lacking. It is found in mountain lakes or in locked off parts of rivers, Ritche ponds (Moselle), upper drainage basins of Aspe and Gaube streams Pyrénées) etc.
2.	The same observations can be made for Salmo irideus which seems to be identical with Salmo gairdnerii. In 39 French departments where artificial restocking with this fish is carried out every year, it does not reproduce; in 7 other departments, cases of reproduction in open waters are doubtful. Three cases only of establishment have been reported, all in small streams: Ariège, Pyrénées orientales, Cantal: they remain to be confirmed. On the other hand, Salmo irideus is established in closed waters: mountain lakes, as the one of Mont-Cenis (Savoie), lake of Ilhéon, near Cauterets (Pyrénées) or locked off parts of streams, as in the upper valley of Aspe stream, etc.
3.	The failure of Salvelinus fontinalis and Salmo irideus in open waters does not seem to be due to bad ecological conditions. Perhaps, in some cases, it must be explained by a lack of density in the initial stocking with young fish. The dangerous competition of Salmo trutta is a more general cause: this species destroys Rainbow Trout eggs which are laid during the spring, at a time when it has recovered from the exhaustion of its own reproduction. But, above all, the great voraciousness of Salvelinus fontinalis and Salmo irideus, which is to be associated with their great capacity of growth, make them be too easily caught by fishermen. Finally, Salvelinus fontinalis is easily injured, frequently liable to diseases, and Salmo irideus, very bold, is exposed, more than Salmo trutta to the too actual dangers of predators and of man.