114 



BULLETIN OF THE BUREAU OF FISHERIES 



6. Dorosoma cepedianum (Le Sueur) 

 Jack shad; Skip jack; " Scissor-bellt shad"; Gizzard shad 



Megalops cepedina Le Sueur, Journ., Ac. Nat. Sci., Phila., I, 1818, p. 361. 



Although of slight value, directly, as a food fish, the jack shad, through utilizing the fine 

 plankton largely neglected by most other fish, furnishes the carnivorous species a valuable source 

 of food. The specialized gill rakers (which, on the first arch, numbered close to 350 in a specimen 

 95 millimeters in standard length) enable it to utilize this microscopic material, which undergoes 

 the first stage of digestion in the thick-waUed gizzardlike stomach. The intestine slightly exceeds 

 the fish in length. Copepods predominated in the seven stomachs examined, with an appreciable 

 quantity of Daphnia and fine vegetation also present. 



Gravid females were taken in June. One of these, 315 millimeters in length, contained 

 approximately 50,000 eggs, being more prolific, probably, than any other fish of the region. 



The jack shad is represented in the collection by 12 specimens, ranging in length from 58 to 

 315 millimeters (2% to 12% inches), collected in a borrow pit along the Itta Bena Road and in a 

 borrow pit at Wakeland. 



Genus ICTIOBUS Rafinesque 



The following key is introduced to show the distinguishing characters noticed 

 by the authors, who experienced some difficulty in identifying the species. 



KEY TO THE SPECIES 



a. Mouth large, oblique; upper lip on or above level of lower margin of eye; lips thin and nearly 



smooth; gill rakers long and numerous, 38 to 55 on first arch cyprinella, p. 114 



aa. Mouth smaller, less oblique to inferior; upper lip much below level of the lower margin of eye; 



lips thickened, more or less striate; gill rakers shorter and only about half as numerous as 



in the preceding. 



b. Back notably elevated and strongly compressed; depth of body (in Greenwood specimens) 

 2.4 to 2.5 in length; vertical distance from origin of dorsal to a straight line running through 

 the center of eye to lateral line on base of caudal equal to or greater than head; ventral out- 

 line from chin to ventrals nearly straight; anterior rays of dorsal strongly elevated, the 

 longest one equal to length of head; mouth small, inferior, more strongly protractile down- 

 ward than forward bubalus, p. 115 



bb. Back less strongly elevated and less strongly compressed; depth of body (in Greenwood 

 specimens) 2.75 to 3.15 in length; vertical distance from origin of dorsal to a straight line 

 running through center of eye to lateral line on base of caudal, notably shorter than head; 

 ventral outline more strongly curved; anterior rays of dorsal shorter, the longest one 1.25 

 to 1.55 in head; mouth a little larger, oblique, protractile forward rather than down- 

 ward urus, p. 115 



7. Ictiobus cyprinella (Cuvier and Valenciennes) 

 Big-mouth buffalo; Red-mouth buffalo; " Gourd-head buffalo " 

 Sckrognathus cyprinella Cuvier and Valenciennes, Hist. Nat. Poiss., XVII, 1844, p 477. 



This common buffalo fish is represented in the collection by 16 specimens ranging in length 

 from 200 to 485 millimeters (8 to 19H inches). Much variation in depth among specimens exists. 

 For example, in two fish, each 250 millimeters in standard length, the depth varies from 82 to 97 

 millimeters. This fish differs from the other species in the large oblique mouth, thin lips, and weak 

 pharyngeal teeth, characters usually given in keys; also in the much more numerous and more 

 slender gill rakers, the first arch supporting 38 to 55 rakers, exclusive of the fleshy ridges on the lower 

 part of the arch, whereas in the other species this arch has only about half that many. Forbes and 

 Richardson (1908, p. 70), however, state that I. cyprinella has 75 gill rakers on the first arch. This 

 appears to show either a wide variation (if the identifications be correct) among individuals or a 

 difference in the number of gill rakers with age. The five specimens from Greenwood examined with 



