3 8 Memoir Sears Foundation for Marine Research 



sent on top of head. Snout in 22 grown specimens (390-700 mm FL), mucii shorter 

 than postorbital distance (av. 70 "/o of the latter), but in a young specimen, longer than 

 postorbital distance (i83"/o). Postorbital distance in adults 51-61 "/q (av. 55'*/o) of 

 hi, but 33''/o in a young specimen. Interorbital width 34— 40*'/o (av. 37%) of hi, and 

 Mouth width (excluding lips) 69-8 i^/q (av. 74''/o) of interorbital width, these two 

 characters not differing with age. 



Gill rakers rather long, triangular, in 13 specimens 22—29 (^v- '^S-S) °" ^'^'^^ 

 branchial arch; in number of gill rakers, A. brevirostris occupies an intermediate 

 position between A. oxyrhynchus with 17-27 (av. 21.5) and A.fulvescens with 25—40 

 (av. 33)- 



Caudal fin with short upper but rather long lower lobe; average difference be- 

 tween TL and FL, i I'/o of FL; no notch at tip of upper caudal lobe. 



Color. In preserved specimens, general color similar to that of A. oxyrhynchus 

 (p. 46). Top of head and back dark, becoming paler on sides ; entire lower surface 

 white. Central part of dorsal shields whitish, contrasting with darkly pigmented back 

 and black skin between shields. Lateral shields pale, clearly distinguished from sur- 

 rounding skin. Ventral shields of the same whitish color as lower surface of fish. Intes- 

 tinal tract, air bladder, and fat surrounding gonads darkly pigmented, nearly black; 

 the peritoneum only slightly pigmented. 



In an excellent photograph of a live brevirostris, the similarity in color to oxyrhyn- 

 chus is particularly striking (^^: 14, 15): in addition to the details observed on preserved 

 specimens, the white edging on the paired fins is similar; but the anal fin in brevirostris 

 is pigmented while that in A. oxyrhynchus remains whitish. Small live specimens from 

 the Hudson River show black pigment blotches similar to those of young A.fulvescens. 



Size: This is the smallest species of all the Sturgeons. Apparently it never grows 

 to more than about three feet; the largest specimen recorded thus far is a female 

 39.5 inches TL (899 mm FL), from the Connecticut River. The measurements sub- 

 mitted by Professor Andrews and two specimens sent to us (p. 40) confirm his deter- 

 minations. The largest sizes encountered during the present studies were: a female 

 34.8 inches TL, weighing eight pounds 15 ounces, in its 13th year as determined by 

 ■its otoliths; and a male 25.5 inches, weighing four pounds five ounces; both were taken 

 from the Hudson River (j5: 68-70). 



Development and Growth. The early life history is unknown. Few small specimens 

 have been recorded; probably the smallest fish is one of 7.3 inches (about 185 mm), 

 from North Carolina (USNM 64330). The smallest specimens taken in the Hudson 

 River were two females; one was 17 inches (about 433 mm) and weighed only 15 

 ounces; the other was a little less than 18 inches (about 600 mm) and weighed 19 

 ounces. The sizes of five specimens from the Delaware River observed by Ryder ranged 

 between 18-23 inches. Age determinations, based on otolith readings (J5: 68-70), 

 have shown that A. brevirostris is a very slow-growing species. Specimens of brevirostris 

 from the Hudson River that measured 17-35 inches (about 430-890 mm) TL were 

 4-15 years old; on the other hand, A. oxyrhynchus 74-100 long were 1 1-13 years of 



