Fishes oftJie JVestern North Atlantic 



47 



2,670 mm TL (60-2,500 mm FL), St. Lawrence River, 

 Quebec, between Three Rivers and Riviere-aux-Outardes.** 



Distinctive Characters. A. oxyrhynchus oxyrhynchus is 

 readily distinguishable from both brevirostris (Shortnose 

 Sturgeon) and fulvescens (Lake Sturgeon) by the arrange- 

 ment of its preanal shields in a double row, by its pale un- 

 pigmented viscera, by a mouth less than 55 "/o as wide as 

 the space between the orbits, and by the presence of a soft 

 area (fontanelle) on the top of its head. It differs from A. oxy- 

 rhynchus desotoi (p. (,€) in that its bony shields are oval and 

 longer than broad, and that the carina on its dorsal shields 

 do not have a conspicuous hook. Among western Atlantic 

 species, furthermore, A. oxyrhynchus has much the longest 

 upper caudal lobe but a rather short lower one. In A. oxy- 

 rhynchus the average difference between TL and FL is i4''/o 

 of FL, in A. brevirostris 11 "jo, and in A. fulvescens <)''/o- 

 For a discussion of the differences between oxyrhynchus and 

 sturio of the eastern Atlantic, see p. 57. 



Description.^^ Scutes strongly developed in all longitu- 

 dinal rows; in 1,814 Quebec specimens, 7—13 (av. 9.8) dorsal 

 shields, and in 692 specimens, 24—35 (^^- 2^-7) lateral 

 shields ; shields behind dorsal fin in pairs ; elongated fulcrum 

 at base of lower caudal lobe decidedly longer than base of 

 anal fin. Dermal ossifications also well developed on skin 

 between dorsal and lateral rows. 



Head elongate. A membranous Fontanelle between 

 frontal and parietal plates in young individuals, and a sinus 

 at all ages. Snout longer than postorbital distance in indi- 

 viduals up to 95 cm, but in older specimens shorter than 

 postorbital distance. Interorbital width rather narrow, var- 

 ying; in 239 young specimens (6—49 cm), 22.4-28.4"/o 

 (av. 26" jo) of hi, in 439 older specimens (50—231 cm), 25— 

 2 5.6° jo (av. 2g°jo). Mouth narrow, its width (excluding 

 lips) less than 55*'/o of interorbital width. 



Gill rakers among specimens from the St. Lawrence 

 River, Quebec (studied by Vladykov and Beaulieu, 83: 43- 



34. For origin, size, and method of fishing, see Vladykov and Beaulieu {83 : 43-47). 



35. In part from Vladykov and Beaulieu {83: 43-47), but mainly from an unpub- 

 lished manuscript by the same authors on the morphometric studies on Quebec 

 Sturgeons. 



Figure 10. Acipenser oxyrhynchus. Lateral view of immature male, 581 mm 

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



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