2022 



The Cornell Reading Courses 



individuals of the same brood and of the same age. It has been observed 

 that the offspring of a single pair of rainbow trout at the age of five months 



varied in length from two to 

 five inches. Some of the 

 variation is due to the 

 greater activity among cer- 

 tain individuals, but there 

 also seems to be some un- 

 known inherent factor. It 

 is therefore very evident that 

 the rate of growth of fishes in 

 any pond is impossible of 

 prediction. A rough idea of 

 what occurs in natural bodies 

 of water can be given, how- 

 ever, which will indicate 

 what it should be the aim 

 to produce or surpass in 

 artificial ponds. 



Fig. i8i. — One of the crustaceans (Simocephalus) 

 eaten by the larger-sized advanced fry. Enlarged 

 twenty-eight diameters 



The data in the table on page 2021 are based 

 principally on investigations of the rate of growth 

 of fishes in natural bodies of water near Ithaca, 

 New York, but some have been secured elsewhere. 

 Included in the table are also the months in 

 which spawning occurs and in which advanced 

 fry and fingerlings are usually available. 



Feeding habits 

 All young fishes are somewhat similar in 

 their feeding habits, subsisting principally on 

 various small animals including the microscopic 

 Protozoa, wheel animalcules, and the smallest 

 Crustacea of which Simocephalus and Cyclops are good examples (Figs 

 181 and 182). 



Fig. 182. — A crustacean 

 (Cyclops) abundant in all 

 stagnant ponds and eaten 

 by all young fishes. En- 

 larged twenty-eight diam- 

 eters 



