4.48 Memoir Sears Foundation for Marine Research 



Dorosoma petenense (Giinther) 1866 



Threadfin Shad 



Figure i i 7 



Siudy Material. Twenty-five specimens, 59-180 mm SL, for measurements, and 

 186 for meristic data except as otherwise stated, from Florida to Lake Peten, 

 Guatemala. 



Distinctive Characters. The terminal mouth and the smooth ventral edge of the 

 upper jaw distinguish this species from the other forms of Dorosoma. In addition it is 



Figure 117. Dorosoma petenense, from Atchafalaya River, Alabama, USNM 48790. After Evermann and 

 KendaU. 



readily separated from D. cepedianum in having larger, regularly arranged scales (fewer 

 than 50 in lateral series), only 40—45 vertebrae, a smaller anal fin with 17—27 rays 

 (usually 20—25), a longer and more pointed snout, longer upper jaw and mandible, 

 and usually 16 or 17 + 9— 11 ventral scutes. This species may be confused with 

 Opisthonema oglinum, since both have a prolonged dorsal filament, but the latter is 

 distinguished by the features given under Remarks in the generic account (p. 443). 



Description. Proportional dimensions in per cent of standard length and head 

 length, with all measurements "stepped off" with precision dividers; based on speci- 

 mens 59-180 mm SL; counts based on 186 specimens or less, the number of speci- 

 mens counted being given in parentheses. 



Body: depth 2.4—3.0 in SL. 



Caudal peduncle: length 2.3—3.4 and 



depth 2.25-2.8 in hi. 

 Head: length 2.95-3.7 in SL; width 



1.95—2.4 in hi. 

 Snout: length 4.1—4.85 in hi. 

 Eye: length 3.3-4.1 in hi. 

 Interorbital: bony width 3.5—4.5 in hi. 



Upper jaw: length 2.8-3.35 ^" ^'• 



Mandible: length 2.1—2.5 '" ^'• 



Dorsal fin: base 1.5-2.05 in hi; length 



of filament 2.7—3.1 in SL, 0.6—1.0 



in hi. 

 Caudal fin: length of lower lobe 0.7-0.9 



in hi. 

 Anal fin: length of base 3.5-4.35 in si. 



