Size and Age of Freshwater Fishes 309 



These specimens were taken during a period of ten weeks in June, 

 July and August. All species studied spawn in late spring or early 

 summer". Their ages at time of collection therefore would be a little 

 more than whole years. The fraction is so small that it was thought 

 advisable to consider the age as whole years. 



Table I indicates that the bluegills of Eagle (Winona) Lake in- 

 crease in length about 77 per cent between the ages of one and two 

 years, about 37 per cent the next year and 16 per cent the next. The 

 increase in weight during the second year is over 900 per cent. The 

 bluegills of Shoe Lake (Table II) however, increase but 24 per cent in 

 length between the ages of two and three years. The small number 

 of specimens may be the cause of this discrepancy or there may be a 

 constant difference in rates of growth in the two lakes. This 

 point needs further investigation with larger numbers of specimens. 



Yellow perch (Table III) showed a length increase of 41.5 per cent, 

 22.7 per cent, and 28 per cent respectively for the years from one to 

 four, and an increase in weight of 119.4 per cent, 108 per cent and 

 157 per cent respectively for the same period. Pearse and Achtenberg' 

 "believe that yellow perch become sexually mature in Lake Mendota 

 (Wisconsin) at the end of two years' growth." Hence if they are to be 

 given a chance to breed one season no perch less than 14 or 15 centi- 

 meters (measured to base of caudal fin) should be taken. 



The numbers of black bass are too few to arrive at any satisfactory 

 conclusions but the data are given m table IV and figure 4. 



It is interesting to note, as a comparative study, the rate of growth 

 of yellow perch in Lake Erie'. The two, three, and four year old perch 

 average respectively 3.3, 3.1, and 1.2 centimeters longer than those Of 

 corresponding ages in Eagle (Winona) Lake. 



This question of rates of growth is very closely linked up to other 

 problems of fresh-water biology. It has a connection with population 

 and food conditions of the lakes. If a species grows more rapidly in 

 one lake than in others it indicates that the food complex is more 

 favorable there. This may mean that the food is more abundant or that 

 competition is less severe. A systematic investigation of rates of growth 

 of the fishes of inland waters will no doubt reveal some very interesting 

 facts on the fertility of our various lakes. From an economic viewpoint 

 it will mean a better knowledge of the possibilities of our lake resources. 



- Forbes, S. A., and Richardson, R. E. The fishes of Illinois. Nat. Hist. Surv. 111., 

 Vol. Ill, 1908. 



' Pearse, A. S.. and Achtenberg, Henrietta. Habits of yellow perch in Wisconsin 

 lakes. Bui. U. S. Bur. Fish, Vol. XXXVI, 1917-18, pp. 297-366. 



■■ Harkness, W. J. K. The rate of growth of the yellow perch iPcrca fldvcsrciifi) in 

 Lake Erie. Uni. Toronto Studies, No. 20, 1922. pp. 89-95. 



