1911 Encyclopædia Britannica/Parr

PARR, a name originally applied to the small Salmonoids abundant in British rivers, which were for a long time considered to constitute a distinct species of fish (Salmo salmulus). They possess the broad head, short snout and large eye characteristic of young Salmonoids, and are ornamented on the sides of the body and tail with about eleven or more broad dark cross-bars, the so-called parr-marks. However, John Shaw proved, by experiment, that these fishes represent merely the first stage of growth of the salmon, before it assumes, at an age of one or two years, and when about six inches long, the silvery smolt-dress preparatory to its first migration to the sea. The parr-marks are produced by a deposit of black pigment in the skin, and appear very soon after the exclusion of the fish from the egg; they are still visible for some time below the new coat of scales of the smolt-stage, but have entirely disappeared on the first return of the young salmon from the sea. Although the juvenile condition of the parr is now universally admitted, it is a remarkable fact that many male parr, from 7 to 8 inches long, have their sexual organs fully developed, and that their milt has all the fertilizing properties of the seminal fluid of a full-grown and sexually matured salmon. On the other hand, no female parr has ever been obtained with mature ova. Not only the salmon, but also the other species of Salmo, the grayling, and probably also the Coregoni, pass through a parr-stage of growth. The young of all these fishes are barred, the salmon having generally eleven or more bars, and the parr of the migratory trout from nine to ten, or two or three more than the river-trout. In some of the small races or species of river-trout the parr-marks are retained throughout life, but subject to changes in intensity of colour.