REPORT OF THE COMMISSIONER OF FISHERIES XLI 



been submitted, and an equally comprehensive study of the syste- 

 matic relationships and natural history of the whitefishes of the 

 Great Lakes has been brought to virtual completion. While the 

 total yield of the commercial fisheries of the Great Lakes region has 

 not declined appreciably in recent years, there has been a noticeable 

 reduction in the take of such valuable species as the whitefishes and 

 ciscoes, their place having been taken by less desirable species. The 

 discovery that whitefishes are divided into numerous species not 

 previously recognized, many of which are extremely localized in their 

 distribution, explains the possibility of depletion of these more val- 

 uable forms. While overfishing is recognized as the chief probable 

 cause of the decline, pollution of the fishing grounds and spawning- 

 areas is considered an important factor. An understanding of the 

 natural history of many of these species now makes possible the 

 formulation of effective regulations for the protection of the fisheries 

 and the agreement upon a policy of protection by the several States 

 and the Canadian Government. 



In response to public interest in the development of the fisheries 

 of the interior waters, the bureau is giving attention to the problems 

 of aquiculture or water farming, such as the improvement of prac- 

 tical fish-cultural practices in Federal and State hatcheries and fun- 

 damental studies in the physiology and nutrition of fishes, the pre- 

 vention or treatment of diseases, and the development of a superior 

 brood stock. Experiments in feeding rainbow and brook trout with 

 the customary foods to which have been added other substances that 

 contain the various vitamins have been conducted, and while the 

 entire significance of apparently conflicting results is not fully under- 

 stood many facts have been adduced. These experiments indicate 

 that each species of trout reacts differently to different feeding ra- 

 tions, that certain commercial foods are of little value, and that the 

 practice in many hatcheries of feeding stale foods is distinctly detri- 

 mental. This work has been conducted on an extended scale at the 

 Holden (Vt.) experiment station, and an analysis of the results is 

 under way. Studies on the treatment and control of fish diseases 

 have been continued, and advice has been given freely by the bureau's 

 pathologist to numerous trout and goldfish producers and to various 

 State and private hatcheries. 



Extensive experiments in pond culture have been undertaken at the 

 Fairport (Iowa) biological station with a view to increasing the 

 productiveness of ponds and of more fully utilizing marshy lowlands 

 as sources of food supply and recreation. The entire pond system of 

 the station is being employed in studies on increasing the food supply 

 of the fish by means of fertilizers and the production of an abundant 

 supply of forage fishes for bass and other carnivorous species. The 

 raising of buffalo fish and bass is being undertaken under semicon- 

 trolled conditions, and detailed observations on environmental fac- 

 tors affecting their growth are conducted regularly. 



Closely correlated with the work in aquiculture are the studies 

 in limnology that are being conducted in cooperation with the Uni- 

 versity of Wisconsin. Highly significant studies on the basic food 

 supply in fresh-water lakes have been made as part of this program, 

 and a report that adds materially to our knowledge of the subject 

 has been submitted for publication. 



