Migrations in the Sea

Abstract

THE terms âœanadromousâ and âœcatadromousâ are employed to distinguish fish which leave the sea to spawn in fresh water and fish which migrate from fresh water to the sea when they reach maturity. Gilson, in his paper, âœL'Anguilleâ (1908, Ann. d. I. Spc. toy, Zool. et Malacca, d Belgique, T. 43), proposed that the words should be used to define migrations to and from fresh water. The salmon, for example, is catadromous as a smolt, anadromous as a grilse, and so on. But unless new terms are to be created the words must be given a much wider significance than Gilson has suggested. The migrations of fish from the lower part of a river to the higher reaches, from a river to a stream, from the deep region of a lake to the shallows only differ in degree from the anadromous migration of the salmon. It cannot be said either that there is any difference requiring a new term in. the migration of a fish from the sea into the lower part of a river or into an estuary. A fish which migrates from relatively deep water to the coast may also be said to have made an anadromous migration. There are species which may spawn in fresh or brackish water, and species which may spawn in salt or in brackish water. In short, it may be said that fishes present every degree of anadromous migration from mid-ocean to the upper limits of streams, and corresponding catadromous migrations. It is now proposed, therefore, that these words should be used to indicate the direction of the migration, however small or great that migration may be, whether passive or active, pelagic or demersal, seasonal or spawning.