26 



THE REPORT OF THE 



No. 36 



THE ECONOMIC IMPORTANCE OF INSECTS AS FOOD FOR THE 



COMMON WHITEFISH 



Wilbert A. Clemens, Department of Biology, 

 University of Toronto 



During the summer of 1921 a field party from the Ontario Fisheries Research 

 Laboratory of the University of Toronto commenced an intensive study of 

 fishery problems in Lake Nipigon. One phase of the investigations has had 

 to do with the food supply for fish in the lake and the percentages of the various 

 food organisms in the diets of the fish as revealed by the examination of stomach 

 contents. Special attention has been given to the common whitefish, Core- 

 gonus clupeaformis , as it is the most important of the commercial fishes taken 

 in Lake Nipigon. 



The writer desires to express his appreciation of the assistance given by 

 Messrs Dymond, Bigelow, Adamstone, and Harkness, who as members of the 

 party assisted in various ways in the work. 



During the first season the stomachs of 209 whitefish were examined. The 

 results show that this fish is almost entirely a bottom feeder and its diet consists 

 chiefly of Chironomid larvae and pupae, snails and small clams, Hoy's fresh 

 water shrimp, Pontoporeia hoyi, mayfly nymphs, caddis larvae, corixids, water 

 mites, Ostracods, terrestrial insects and occasionally small fish such as ciscoes, 

 sticklebacks and miller's thumbs. The following examples will illustrate*: 



Whitefish 



Shrimps 

 {Pontoporeia) 



Caddis 

 larvse 



Chironomidce 



Snails 



Miscellaneous 



size 



larvae 



pupae 





14.0 cm. 







80% 



10 



6 



4 



14.5 



20 





30 



5 



25 



20 



22.0 







2 



85 





13 



28.0 



30 





70 









35.0 





2 



3 





15 



75 (fish) 

 5 (misc.) 



35.0 













70 (terrestrial insects) 

 30 (misc.) 



37.0 



50 





40 





10 





38.0 



25 





25 



3 



40 



7 (Mayfly Nymphs, 

 etc.) 



40.0 









3 



2 



95 (terrestrial insects) 



45.0 











99 



1 (terrestrial insects) 



It is evident that the insects form very important items in the food of the 

 whitefish. Calculations for the 209 fish examined show that they constitute 

 53 per cent, of the food — roughly 50 per cent. Chironomids, particularly the 

 larvae, are by far the most important of the insects and constitute 35 percent, of 

 the food of the whitefish, while mayfly nymphs form approximately 6 per cent., 

 terrestrial insects 6 per cent, and miscellaneous insects such as caddis larvae, 

 corixids etc. 3 per cent. 



These percentages are particularly significant when the catch of whitefish 

 is considered. In 1919 (the latest available statistics) 1,620,970 lbs. of white- 

 fish were taken from Lake Nipigon. At the wholesale price to the fisherman of 

 10c per lb., the value of this catch was $162,097. It appears to be a reasonable 



*The stomach contents of 65 whitefish are described in detail in a paper now in press, Uni- 

 versity of Toronto Studies, Publications Ont. Fish. Research Laboratory, by Messrs. Clemens, 

 Dymond, Bigelow, Adamstone and Harkness. 



