172 NATURE STUDY REVIEW [10:5— May, 1914 



RATE OF GROWTH 



There is considerable individual variation in the growth of all 

 fishes, even when they are living apparently under identical 

 conditions. For this reason, it is impossible to predict just how 

 large a fish will be at a certain age. 



The writer has only a few data to offer concerning the chub 

 covering a period of about nine months from the date of hatching. 

 In the manner referred to heretofore, eggs were collected and 

 hatched indoors. When the young began to feed, they were 

 placed in a small pond approximately 3x8 feet provided with 

 plenty of aquatic plants and minute organisms but destitute 

 of fishes. At different times a few young fishes which seemed 



Fig. 2. Chub 7 days old. Yolk sac nearly absorbed. 



m, mouth; p, pectoral fin; a, anal fin in formation. 



Length 3 1 inches. Magnification 1 1 diameter. 



to be of average size were taken out and measured with the follow- 

 ing results : 



May 22 (1913) May 28 July 29 Feb. 26 (1914) 



Just hatched 7 days 67 days 280 days 



Length in inches .22 .31 1.38 2.5 



How large chubs will be at the end of the second or any subse- 

 quent year and at what age they first begin to breed, are interesting 

 questions which, so far as the writer can find, have never been 

 determined. 



FOOD 



The study of a fish's food is always interesting. In the chub 

 it seems to vary to a certain extent with the age of the fish and with 

 the kind of food available in the particular spot where the chub 

 lives. As stated heretofore when the fish is first hatched it car- 

 ries its own food supply in the yolk sac. But in three to seven 

 days this is used up and the young swim towards the surface 

 where they may seize almost any minute particles floating by. 

 In the stomachs of such young fishes the writer has found diatoms 

 and a few other minute plant forms, small protozoa, and the 

 smallest crustacean animals such as minute species of copepods. 



