86 



NORTHERN FISHES 



Figure 5. Fresh-water dogfish, Amia calva. male, 18 inches long. 



Figure 6. Fresh-water dogfish, Amia calva, female, "20 inches long. 



and gulping in a fresh supply. They are very tenacious of life; speci- 

 mens have been kept out of water at low temperatures for 24 hours 

 without apparent harm. Young dogfish have been highly recommended 

 as bait because they will live for hours on a hook, but this practice 

 should be discouraged to avoid introducing this destructive species into 

 lakes where it is not now present. 



The dogfish is voracious, feeding on all kinds of animal life, though 

 fishes, including its own kind, form a large part of its diet. It is destruc- 

 tive of game fishes and forage fishes alike. It often feeds at night. Those 

 in the aquaria at the University of Minnesota do not feed much during 

 the winter, though in some northern lakes a dogfish will occasionally 

 bite on a hook in the winter. 



Spawning occurs in May or early June. Sometimes the dogfish migrate 

 in large numbers up small streams or into weedy bays of lakes. The 

 males at this time assume brighter colors, particularly of the fins, which 

 become a bright green. A 5-pound female 19 inches long had '■23,600 

 eggs in the ovaries. A 21-inch female had 64,000 eggs in the ovaries. 



A nest is prepared by hollowing out a depression in the mud or sand 

 until a firm bottom is obtained. Any plants present are torn away until 

 the rootlets are exposed. Spawning usually takes place at night, the 

 male guarding the nest. The young at first adhere to rootlets on the 

 bottom of the nest by an adhesive organ on the snout. When the young 

 can leave the nest they travel in dense schools, guarded for some time 

 by the male. The young, like those of the gar, have at first a lance- 



