450 Memoir Sears Foundation for Marine Research 



and similar obstructions, and large aggregations are seen at reservoir inlets. Water 

 current obviously attracts large schools; when the electric turbines were reduced or 

 shut off in the Tennessee impoundments, the Threadfin Shad were difficult to find, 

 but when the power was turned on they were present in abundance. 



Food and Feeding. Like their close relative, these fish are plankton feeders, the major 

 items of the adult diet consisting of algae (diatoms and unicellular green species), cope- 

 pods, and cladocerans. Threadfin Shad introduced into the Salton Sea, California, have 

 a preference for the fry of Bairdiella icistius (Jordan and Gilbert), which suggests that 

 they may have similar food habits in coastal lagoons and estuaries within their natural 

 range. 



Tolerance to Temperature. As in the case of the gizzard shad, sudden temperature 

 changes often produce high mortality among Threadfin Shad. Berry et al. have observed 

 a spawning mortality for both species during April in Florida lakes. D. petenense cannot 

 tolerate as low temperatures as D. cepedianum. For Threadfin Shad in the Colorado 

 River, Texas, temperatures of about 54—58° F may be close to the minimum tolerance. 

 However, among experimental individuals from the lower Tennessee River, subjected 

 to water cooled from 50 and 60° F, there was a high mortality below 45°, with very 

 few fish surviving below 40°. 



Habitat and Occurrence. Threadfin Shad seek habitats similar to those of the gizzard 

 shad and are often associated with Z). cepedianum where the two species are sympatric. 

 They live in bays, large rivers, reservoirs, lakes, estuaries, and other similar situations. 

 Along the coast of Texas they occur in bays having salinities varying from 3.8 to 

 26.9 '/oo) the majority having been taken in waters with salinities between 10 and 

 20«/oo. Apparently these fish show a preference for water that is neither fully marine 

 nor very fresh, a condition typical in many lagoons along the coast of Texas. Larger fish, 

 approximately 100— 150 mm long, occurred in waters of about 15— 3o''/oo, whereas 

 smaller fish, generally below 100 mm, were taken in salinities below 15 "/oo- 



Records of Threadfin Shad obtained by Dr. R. D. Suttkus through 1958 indicate 

 their occurrence at nearly 50 brackish and saltwater stations in Florida, Alabama, 

 Mississippi, Louisiana, and Texas, not including about 75 captures from Lake Pont- 

 chartrain. 



Range. From the Ohio River of Kentucky and southern Indiana westward and 

 southward to Oklahoma, Texas, and Florida, thence along the coast of the Gulf of 

 Mexico to northern Guatemala and British Honduras (Belize River). Their recent in- 

 vasion of the Ohio River Basin is discussed by Minckley and Krumholz (9<^). 



Synonyms and References: 



Meletta fetenemis Giinther, Proc. zool. Soc. Lond., 1866: 603 (orig. descr.; Lake Peten, Guatemala). 



Chatoessus petenensis Giinther, Cat. Fish. Brit. Mus., 7, 1868: 408 (redescr. of types). 



Chatoessus mexicanus Giinther, Cat. Fish. Brit. Mus., 7, 1 868 : 409 (orig. descr.; Mexico, New Orleans, Louisi- 

 ana). 



Dorosoma mexicanum Jordan and Evermann, Bull. U.S. nat. Mus., 47 (i), 1896: 416 (descr., from Giinther). 



Dorosoma petenense Jordan and Evermann, Bull. U.S. nat. Mus., 47 (i), 1896: 417 (descr., from Giinther); 

 Regan, Biol. Centr. Amer., Pisces, 8, 1906-08: 178 (redescr. of types) ; Fowler, Proc. Acad. nat. Sci. 



