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The American shad (''Alosa sapidissima''), is a species of anadromous clupeid fish naturally distributed on the North American coast of the North Atlantic, from Newfoundland to Florida,〔 and as an introduced species on the North Pacific coast. The American shad is not closely related to the other North American shads. Rather, it seems to form a lineage that diverged from a common ancestor of the European taxa before these diversified 〔Faria, R.; Weiss, S. & Alexandrino, P. (2006): A molecular phylogenetic perspective on the evolutionary history of Alosa spp. (Clupeidae). Molecular Phylogenetics and Evolution 40(1): 298–304. 〕 The American shad has been described as "the fish that fed the (American) nation's founders".〔 Adult shad weigh between and and they have a delicate flavor when cooked.〔"Grass Shad-another Fine Bait- Southeastern King Mackerel Club – King Mackerel Fishing in Southeastern North Carolina." Southeastern King Mackerel Club – King Mackerel Fishing in Southeastern North Carolina-. Web. 15 Dec. 2011. ==Life history== The shad spends most of its life in the Atlantic Ocean, but swims up fresh rivers to spawn.〔 Northern populations are iteroparous, thus they may survive breeding, return to the sea and then return to freshwaters to spawn several more times. However, southern populations exhibit semelparity, similar to Pacific salmon. In the marine environment, shad are schooling fish. Thousands are often seen at the surface in spring, summer, and autumn. They are hard to find in the winter, as they tend to go deeper before spawning season in the range 13-18 °C.; they have been pulled up in nets as deep as . Like other herrings, the American shad is primarily a plankton feeder, but will eat small shrimp and fish eggs. Occasionally they eat small fish, but these are only a minor item in their general diet.〔 The sexually mature fish enter coastal rivers in spring or early summer, usually when the river water has warmed to . Cooler water appears to interrupt the spawn. Consequently, the shad run correspondingly later in the year passing from south to north along the coast, commencing in Georgia in January; in March in the waters tributary to Pamlico and Albemarle Sounds; in April in the Potomac; and in May and June in northern streams generally from Delaware to Canada.〔 In large rivers, such as the Connecticut, American shad run far upstream. The apparent longest distance is in the St. Johns River of Florida, an extremely slow (1" drop per mile, 1.5 cm per km) river that widens into large lakes; shad have been found upriver.〔 The spawning fish select sandy or pebbly shallows and deposit their eggs primarily between sundown and midnight. Females release eggs in batches of about 30,000 eggs, though it has been estimated that as many as 156,000 eggs are deposited by very large fish. Total annual egg production is 200,000–600,000 eggs per female with larger fish producing more. In rivers north of Cape Fear the spent fish, now very emaciated, return to the sea immediately after spawning. In southern rivers, most shad die after spawning. The eggs are transparent, pale pink or amber, and being semi-buoyant and not sticky like those of other herrings, they roll about on the bottom with the current. The eggs hatch in 12 to 15 days at , in 6 to 8 days at , which covers the range characteristic of Maine and Bay of Fundy rivers during the season of incubation. The larvae are about 9 to 10 mm long. Juvenile shad remain in the rivers until fall, when they move down to salt water; they are now 1½ to 4½ inches (70 to 110 mm) long, resembling their parents in appearance. They prefer open waters and temperatures in the range 13-18 °C. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「American shad」の詳細全文を読む スポンサード リンク
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