26 ILLINOIS BIOLOGICAL MONOGRAPHS [26 



A very common species in practically every lake of any size in the 

 county. An inhabitant of weed beds, the dogfish is found most commonly 

 just over the edge of the bars where heavy beds of Potamogeton offer a 

 congenial environment. Breeding begins early, probably often late in 

 April but more frequently early in May, the nesting site preferred being 

 weed beds in water from three to five feet in depth. As I have seen many 

 nests guarded by the parent fish, I conclude with Reighard that it is always 

 the male that protects the nest and guards the young after they leave the 

 nest. The eggs hatch in from nine to twelve days, depending upon the 

 water temperature, and the young fish remain for a little over a week within 

 the confines of the nest. Thereafter they all leave the nest together, 

 traveling in a compact mass and zealously guarded by the very pugnacious 

 male. As the young grow, the compactness of the school slowly lessens 

 until, when the young are nearly four inches long, the mass formation 

 disappears and the young go about their business on their own responsi- 

 bility. While guarding the young, the male dogfish will attack anything 

 that threatens the precious mass of youngsters. I have had the parent 

 attack nets, rakes, sticks — anything I thrust toward the ball of young; 

 a vicious attack, a strike at the intruding object, and a dash away to a 

 distance of about six feet; a swift turn and another vigorous attack. 

 During this performance by the old fish, the school breaks up in every 

 direction, the young going to the bottom and scurrying toward deeper 

 water under the protection of the vegetation. The food consists entirely 

 of animal matter, varying between fish and crayfish at different seasons 

 of the year, the late summer and fall finding the latter the dominant food. 

 Among the fish, over and above many species of minnows, which I have 

 taken from the stomachs are : Lepomis pallidas, Lepomis gibbosits, Micro p- 

 terus salmoides, M. dolomieu, Perca flavescens — in fact, small specimens of 

 all of the game or food fishes. Economically, then, inasmuch as the dog- 

 fish is never considered as of any food value in this region, it must be 

 classed as a species destructive of game fish. Commercial fishermen always 

 destroy every gar and dogfish they catch in their nets. The species attains 

 considerable size, specimens that I have taken weighing as high as eight 

 pounds. 



Order ISOSPONDYLI 

 Family salmonidae 

 3. Coregonus alb us (Le Sueur). Whitefish. 



The whitefish is not a native of the inland lakes, and is included in this 

 list because an attempt was made to introduce the fish, an effort which was 

 only temporarily successful. In 1887, according to the report of the game 

 warden department, 350,000 whitefish were planted in Oconomowoc lake. 

 Nothing was seen of the fish for several years. About 1891 whitefish were 



