Genus Dorosoma Rafinesque 1820 



Gizzard Shads, Threadfin Shad 



By 



Robert Rush Miller 



Museum of Zoology 

 The University of Michigan 



Dorosoma Rafinesque, West. Rev. misc. Mag., 2(3), 1820: 171 (see Fowler, Monogr. Acad. nat. Sci. Philad., 

 7, 1945 : 6, 8); Ichthyol. Ohiensis, 1820: 39; type species by monotypy, D. notata equals D. cepedianum 

 (LeSueur). Below falls of Ohio River. 



Generic Synonyms: 



Chatoessus Cuvier, Regne Anim., ed. 2, 2, 1829: 320, in part; restricted by Cuvier and \'alenciennes to Megalops 



cefediana LeSueur. 

 Signalosa Evermann and Kendall, Bull. U. S. Fish Comm. (1897), IJ, 1898: 127; type species, Signalosa 



atchafalayae equals D.petenense (Giinther). Atchafalaya River, Melville, Louisiana. 



Characters. Body compressed, silvery. The abdomen armed with Bony scutes; 

 total 23-32. Scales cycloid, thin, 40-83 along side. Mouth small to moderate in 

 size, terminal, subterminal, or inferior, the lower jaw included or jaws subequal. Snout 

 short and rounded. Maxillary with two supramaxillary bones. Teeth absent in adult, 

 but a row of fine teeth on upper jaw in young. Dorsal with last ray prolonged into a 

 slender filament (absent or inconspicuous in young), thus resembling Opisthonema. 

 Fin rays: dorsal 9-15, anal 17-38, pelvic 8, pectoral 12-17, caudal 19 (17 branched), 

 rarely 17 or 18. Stomach gizzard-like, the Intestine long and much convoluted, 

 with numerous Pyloric caeca. Vertebrae (including urostyle) 40-51. 



Remarks. Dorosoma may be readily distinguished from Opisthonema in having 

 (i) the ridge of the back before the dorsal fin naked rather than crossed by scales; 

 (2) no bilobed dermal fold on the vertical anterior edge of the cleithrum; (3) an axil- 

 lary scale, the pectoral fins not folding into a groove; (4) the dorsal origin not well in 

 advance of the insertion of the pelvic fins; and (5) gill rakers 200-400 in Dorosoma, 

 only about 65—109 in half-grown to adult Opisthonema. 



Range. All species except D. smithi are confined to the Atlantic drainage of North 

 and Middle America, from Canada to Nicaragua. They are found from southern South 

 Dakota, Nebraska, and Minnesota, from the Great Lakes-St. Lawrence River Basin, and 

 from about 40 to 41° N on the Atlantic seaboard (New York, New Jersey, and south- 

 eastern Pennsylvania) southward to Lake Nicaragua, but with a discontinuous distri- 

 bution from northern Guatemala and British Honduras to Nicaragua. D. smithi is 

 known only from coastal streams of northwestern Mexico, in Sonora, Sinaloa, and 

 Nayarit. Only two species, D. cepedianum and D. petenense, have been taken in brackish 

 and salt water — the former from as far north as Sandy Hook Bay, New York, south- 

 ward to the vicinity of Tampico, Mexico. 



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