PROGRESS IN BIOLOGICAL INQUIRIES, 1921. 



13 



University of Michigan. The deep-water forms, as the blackfin 

 {Leucichthys nigripinnis) ^ were found to feed almost exclusively 

 upon the crustacean Mysis relicta^ probably the only available food. 

 The deep-water race of the bloater {Leucichthys hoyi) feeds chiefly 

 on Mysis, while a 30-fathom race eats for the most part another lake 

 crustacean, Pontoporeia hoyi. The food of the shallow-water forms 

 is much more varied. The pilot or menominee {Prosopium quadri- 

 laterale) is strictly a bottom feeder, subsisting on mollusks, insect 

 larvae, crayfishes, etc. The whitefish {Ooregonus clupeaformis) is 

 also a bottom feeder, but its food is, on the average, not so coarse as 

 that of the pilot, consisting largely of insect larvae, as those of the 

 mayflies Hexagenia and Ephemera. The lake herring feeds in part 

 upon the same animals, in part upon the minute Crustacea of the 

 plankton. In reference to their available food supply the deep- 

 water forms are absolutely competitive (more so perhaps than any 

 other group of fishes), while the shallow- water forms are only in part 

 competitive. It is probable, however, in view of the former greater 

 abundance of these fishes, that sufficient food exists in the lakes to 

 support a larger population of all the species of whitefishes, 



FISHES OF WISCONSIN LAKES. 



The food and distribution of the fishes in certain Wisconsin lakes 

 have been studied by Dr. A. S. Pearse,* The results indicate that 

 in summer fishes are generally more abundant as conditions ap- 

 proach those in swamps and are fewest when the environment is 

 most like that in rivers. When food is present in quantity and when 

 other conditions are favorable, there are more fishes per unit area 

 in certain inland lakes than in the Mississippi River or in Lake 

 Michigan. Lakes produce considerable food supplies within them- 

 selves, while rivers are more dependent on swamps, ponds, and other 

 tributaries. The factors of importance in limiting the distribution 

 of fishes are discussed (shores, turbidity, depth, bottom, height of 

 water, currents, etc.). An abundant supply of food and vegetation 

 permits many fishes to exist in a lake, but other favorable conditions 

 must be present in order that they may grow to large size. 



A statistical study of the infection of fishes by parasites has been 

 made, the Mississippi and St. Lawrence drainage systems being 

 compared, and various tj^pes of lakes studied. The results are now 

 being tabulated and will soon be ready for publication. A short 

 paper on the habits of the mud puppy, in which its relations to fishes 

 are discussed, has been published.^ 



In order to secure information on the rate of growth of cold- 

 blooded animals in natural conditions, attempts are being made to 

 recover the fishes and turtles tagged and released in Lake Mendota 

 during the summer of 1919. Some specimens have already been 

 secured. 



Studies on the metabolism of fishes are being continued. In this 

 connection quantitative analyses are being made to show the water, 

 ash, nitrogen, and ether extractives of fishes at various stages of 

 growth. 



* Pearse, A. S. : The Distribution and Food of the Pishes of Three Wisconsin Lakes in 

 Summer. University of Wisconsin Studies in Science, No. 3„ June, 1921, 60 p. Madison. 



^ Pearse, A. S. : Habits of the Mud-Puppy Necturus, an Enemy of Food Fishes. Bureau 

 of Fisheries, Economic Circular No. 49, issued May 16, 1921, 8 p. WasJiington. 



