228 Sharks 



spawns. Spawning takes place on stony or pebbly bottoms. 

 The male and female make a "nest" for the eggs by re- 

 moving pebbles from the nesting site with their sucker-like 

 mouths until an irregular depression about 6 inches deep 

 and 2 or more feet in diameter is formed. The adults die 

 after spawning. Actually, once they enter the streams and 

 rivers and their gonads ripen, their digestive system de- 

 generates and they can no longer assimilate food. 



The eggs hatch into small, blind, toothless animals 

 called ammocoetes. These ammocoetes burrow into the 

 mud and live on the microscopic animals in the upper part 

 of the bottom mud. They remain in the mud for about 

 3 to 4 years, reaching a length of about 6 inches. About 

 this time the eyes develop and the sucking mouth is 

 formed, and the lamprey now moves down to sea and starts 

 to feed on the blood of fish. 



Economic Importance: Impassable dams have drastically 

 reduced the population of Sea Lampreys along the coast. 

 Formerly this species was used for food, but few are now 

 taken for this purpose. In recent years the landlocked form 

 of this animal has spread through man-made channels 

 into the Great Lakes where it has reportedly reduced the 

 populations of the most important food fishes, particularly 

 the lake trout. 



SHARKS 



Characters: Sharks are fish-like vertebrates with well de- 

 veloped jaws and bony teeth. The skeleton consists of 

 cartilage. The skin is covered with small, tooth-like enamel 

 projections (denticles). There are 5-7 gill slits on each 

 side of the head. The gill slits open separately to the out- 

 side of the body. All or part of the gill openings are on 

 the sides of the body. 



General Information: The body is usually torpedo-like but 

 in a few exceptional species is flattened. Sharks are widely 

 distributed from the subpolar to the tropical zones. They 

 are mostly found in salt water, but some species enter 

 brackish and even fresh water. 



