42 



Memoir Sears Foundation for Marine Research 



Caudal fin with rather short upper but long lower 

 lobe; the average difference between TL and FL g^/o of 

 FL; no notch at tip of upper lobe. 



Color. There is a pronounced difference between the 

 young and the adult. In young below 300 mm (12 in.) FL, 

 two pairs of large black blotches present on anterior half 

 of upper surface of snout and on back between dorsal and 

 lateral rows of shields, the anterior blotch the larger and 

 immediately behind the base of pectoral fin, the smaller 

 posterior one below the dorsal fin;" in addition, several 

 small, irregular, black spots on top of head, on back and 

 sides, and on lower surface of caudal peduncle. Intestinal 

 tract darkly pigmented, nearly black. Air bladder and fat 

 surrounding gonads, dark gray. Peritoneum pale or only 

 slightly pigmented. In general, the dark pigmentation of the 

 intestinal tract is similar to that of A. brevirostris but very dis- 

 tinct from that of A. oxyrhynchus. In half-grown specimens 

 up to about 24 inches or 610 mm FL, the large blotches 

 have disappeared, but black spots may persist. Older in- 

 dividuals above 40 inches FL are uniformly dark brownish 

 or grayish on top of head and on back and sides. In fish of 

 all ages, dorsal and lateral shields of the same color as back- 

 ground; shields of ventral rows sometimes pigmented on 

 upper part but always whitish on lower part. Lower surface 

 of young and adults uniformly whitish. In young below 24 

 inches FL or about 610 mm, preserved in 4— 5''/o formalin, 

 lower surface and sides of head and body clear green. 

 At all ages, fins dark brown or gray, typically without 

 white edging. 



Size and Growth. Among western North Atlantic spe- 

 cies, A. fulvescens reaches a size exceeded only by A. oxyrhyn- 

 chus. The largest recorded is a female Lake Sturgeon, of 

 approximately 275 pounds, taken in Lake Winnipeg, Mani- 

 toba, in the summer of 1941 {40: 17). The largest male, 

 caught in Lake Erie in 1948, weighed 220 pounds {66: 7). 

 The specimens from Quebec listed in Study Material, 2.5—90 

 inches TL, weighed 0.032 ounces-212 pounds (0.9 g-96 



27. For a good illustration of these black blotches in young A. fulvescens, see 

 Forbes and Richardson (jj: 36); for color illustrations of an adult, see Vla- 

 dykov {82: 6). 



Figure 9. Acipenser fulvescens. Lateral view of immature female, 655 mm 

 long, from the St. Lawrence River near Neuville, Quebec, P. Q., Canada. 



