2o8 Collct/e of Pnrcslry 



ber or November. Petersen ('ii, p. 4) stales that he found 

 the marine bottom fauna of the Kattegat and Baltic Sea to 

 remain relatively unchanged for a period of twenty years. 

 This should l)e borne in mind wlien the time comes to com- 

 pare quantitative data covering several years in the investi- 

 gation of lakes. 



Daily Consumption of Food by Fish 



These quantitative investigations naturally lead to certain 

 questions, such as, How much food does a fish consume in 

 24 hours? How many fish will a body of water like Lower 

 South Bay sustain, with the (juantity of fish food present indi- 

 cated by the data presented in the previous pages? These 

 questions are complicated by the fact that some fish eat vege- 

 table matter and detritus almost entirely, while others include 

 this material as only a part of their diet and there are many 

 other factors, as season, age, etc. The average percentages 

 of different classes of food eaten by our fresh water fish are 

 shown below (Baker, '16, p. 154) : 



Insect 40 percent 



Crustacean 14 " 



Molluscan 6 



Detritus and plants 20 " 



Fish 20 



Total 100 " 



It will be seen that but 60 percent of the food consists of the 

 invertebrates under consideration in this report, and 20 percent 

 more includes the detritus and plants or about 80 percent of 

 the food of our fish. 



The difficulty of ascertaining in a satisfactory manner the 

 amount of food eaten by a fish in a given length of time 

 (as in 24 hours) is obvious. Petersen realized this difficulty 

 and experimented with the marine fish known as Plaice 

 {Pleuronectes platessa Linn.) to find the amount of food eaten 

 in 24 hours upon which to form a basis for calculations relat- 



