SHAD, the name given to certain migratory species of herrings (Clupea), which are distinguished from the herrings proper by the total absence of teeth in the jaws. Two species occur in Europe, much resembling each other one commonly called allis shad (Clupea alosa or Alosa vulgaris), and the other known as twaite sha.d(Clupeafintaoi Alosa finta). Both, like the majority of herrings, are greenish on the back and silvery on the sides, but they are distinguished from the other European species Clupea by the presence of a large blackish blotch behind the gill-opening, which is succeeded by a series of several other similar spots along the middle of the side of the body. So closely allied are these two fishes that their distinctness can be proved only by an examination of the gill-apparatus, the allis shad having from sixty to eighty very fine and long gill-rakers along the concave edge of the first branchial arch, whilst the twaite shad possesses from twenty-one to twenty-seven stout and stiff gill-rakers only. In their habits and geographical distribution also the two shads are similar. They inhabit the coasts of temperate Europe, the twaite shad being more numerous in the Mediterranean. While they are in salt water they live singly or in very small companies, but during May (the twaite shad some weeks later) they congregate, and in great numbers ascend large rivers, such as the Severn (and formerly the Thames) , the Seine, the Rhine, the Nile, etc., in order to deposit their spawn. A few weeks after they drop down the river, lean and exhausted, numbers floating dead on the surface, so that only a small proportion seem to regain the sea. At Elbeuf on the Seine above Rouen there was formerly a hatchery for the artificial propagation of shad. The eggs are spawned in May and June, and are similar in the two species; they are heavier than the fresh water in which they develop, but unlike the herring's eggs they are not adhesive. They remain free and separate at the bottom of the river, carried down by the current or up by the tide. In the Elbe the twaite shad spawns below Hamburg, the allis shad above Dresden. In November the fry have reached 3 to 5 in. in length, but very few specimens in their second year have been found in rivers. The majority seem to descend to the sea before their first winter, to return when mature. On rivers in which these fishes make their periodical appearance they have become the object of a regular fishery. They are much esteemed on the middle Rhine, where they are generally known as " Maifisch." The allis shad is caught at a size from 15 to 24 in., and is better flavoured than the twaite shad, which is generally smaller.
Other, but closely allied species, occur on the Atlantic coasts of North America, all surpassing the European species in importance as food-fishes and economic value, viz., the American shad (Clupea sapidissimd), the gaspereau or ale-wife (C. mattowocca orvernalis), and the menhaden (C. menhaden).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)