$0 ILLINOIS STATE ACADEMY OF SCIENCE 



made at the University of Illinois on certain Illinois 

 fishes. 



Information that is not only interesting but that may 

 be quite important becomes available when one can learn 

 readily the age of fishes collected in various kinds of 

 habitats. Two year old yellow perch from a small lake 

 in northern Michigan are only two-thirds as long as 

 perch of the same age from Lake Erie, and a five year 

 old perch from the former lake may be scarcely as large 

 as a three year old one from the Great Lakes. A law 

 fixing the same minimum size of perch that may be 

 taken from the two kinds of situations cannot be equally 

 well adapted to both. A decision concerning the planting 

 of young fish of any particular kind into a certain body 

 of water might reasonably be greatly influenced by a 

 knowledge of the rate of growth of that kind of fish in 

 such a body of water. 



Scale studies also permit a fairly close approximation 

 to the size which any individual fish had attained at the 

 times when its various winter marks were formed. 



