SOFT-RAYED BONY FISHES 89 



together to form a strong spine. The axis of the tail is bent 

 upwards, so that the upper lobe of the caudal fin is reduced to 

 a row of spines and the lower lobe is well developed. The 

 body is armed with 5 lengthwise rows of large bony scutes or 

 bucklers, 1 along the back, 1 along the middle of each side, 

 and 1 along the lower part of each side ; between these scutes 

 are small scattered denticles. The upper lobe of the tail is 

 covered with rhombic scales, representing the vestiges of the 

 primitive ganoid scales. There is a large air-bladder, which 

 is connected with the gullet by a duct. The coloration is 

 usually olive green, greyish, or brownish purple on the back, 

 replaced by white below the row of scutes along the side. 

 The young sometimes have some small dark spots. 



Sturgeons are found in the seas, estuaries and rivers of 

 Europe, northern Asia and North America. Fossil remains 

 (scutes, pectoral spines and fragmentary bones) date back to 

 the Eocene period. 



The largest species, the Russian Sturgeon or Beluga 

 (Acipenser huso), grows to a length of more than 14 feet and a 

 weight of more than 2000 lb. 



About twenty species of Acipenser are recognized, but only a 

 few of these are of large size. The Common Sturgeon (A. 

 sturio) inhabits the coasts and rivers of eastern North America 

 and of Europe from Scandinavia to the Black Sea ; the 

 Russian Sturgeon or Beluga {A . huso) is common in the Black 

 Sea, Sea of Azov and the Caspian Sea ; the Transmontane, 

 White, Oregon or Sacramento Sturgeon (A. transmontanus) is 

 found on the Pacific coast of North America from Monterey, 

 California to Alaska, and ascends the Sacramento, Columbia 

 and Fraser Rivers. These three represent the largest species. 



Most of the Sturgeons are found both in salt and in fresh 

 water, spending the greater part of their lives in the sea and 

 entering the rivers only for spawning purposes. In some of 

 the large lakes and rivers of North America, however, there 

 are species that have become permanent residents in fresh 

 water. They are an extraordinarily variable group of fishes, 

 and also undergo considerable changes with growth. Further, 

 the different forms tend to cross with one another at times, so 

 that considerable difference of opinion exists among experts 

 as to the number of species that should be recognized. 



