24 U. S. BUREAU OF FISHERIES, 



of fishes, assisted to a limited extent by the bureau. These studies 

 include investigations on the amount of natural food consumed, 

 the chemical composition, the functions of the swim bladder, and 

 the digestive enzymes of fishes. In the investigations on the chemical 

 changes in trout and perch during growth the protein, fat, water, 

 and ash have been determined for fish of various ages taken at inter- 

 vals throughout the year. The composition of fed and starved 

 pumpkinseeds (sunfish) has also been determined and compared 

 with individuals caught fresh from Lake Mendota. 



Studies on the function of the swim bladder have demonstrated 

 that it is primarily a hydrostatic organ that has secondarily taken 

 on respiratory functions. The effects of temperature and pressure 

 on the gaseous content of the organ have been thoroughly inves- 

 tigated. 



A study of the digestive enzymes of fish has been begun and prom- 

 ises to yield results of great value. Up to the present the work has 

 been confined to pickerel, carp, and perch, but it is planned to 

 broaden the scope of the investigation in the future. 



Professor Pearse and his students have also started investigations 

 directed at certain fundamental problems relating to the metabolism 

 of cold-blooded vertebrates that promise to be of exceptional interest. 

 It is planned to use turtles for these investigations, and special 

 attention will be paid to the relation of various rations to the rate of 

 growth ; the relation of temj)erature to pulse, respiration, and hiber- 

 nation ; the basal metabolism ; the amount of food required per day ; 

 the cliemical composition of turtles at various seasons and ages ; and 

 the degree of activity at various temperatures. 



During the latter part of the fiscal year a series of experiments for 

 developing a more satisfactory diet for trout was inaugurated at 

 the Manchester (Iowa) station. For many years there has been 

 little change in the character of the food used at trout hatcheries, 

 although in the light of the moie recent knowledge of animal nutri- 

 tion that has attracted much attention in late years it is evident 

 that the standard rations are deficient in certain essential food re- 

 quirements. They are especially lacking in salts and vitamines, and 

 it is not impossible that many of the difficulties experienced at the 

 hatcheries are in reality primarily due to an inadequate diet. For 

 this reason it was thought advisable to undertake an extensive series 

 of feeding experiments in the hope that it would be possible to work 

 out a more satisfactory ration than those in use at present. Milton 

 C. James, scientific assistant, has been assigned to this work, which 

 was just getting under way at the end of the fiscal year. 



EXPERIMENTAL WORK IN FISH CULTURE. 



A number of investigations relating to the development and im- 

 provement of methods of artificial culture of some important food 

 fishes have been conducted at the Fairport biological station. Ob- 

 servations on the culture of buffalofish seem to indicate that the fish 

 will not lend itself to cultivation on a commercial scale on account 

 of the large acreage necessary for it to attain an optimum growth. 

 Efforts to artificially propagate the paddlefish have not yet succeeded 

 owing to the fact that the young fish placed in one of the ponds sev- 

 eral years ago have not yet reached the age of sexual maturity. They 



