PROGRESS IN BIOLOGICAL INQUIRIES, 1922. 9 



therefore in the intervals at which they should be stripped. Fre- 

 quency of stripping must be determined by experience at each sta- 

 tion and for fish of different conditions. 



Attempts to strip a fish too soon may result in displacing eggs 

 prematurely from the stroma, with the result that they become of 

 the familiar hard glassy type and incapable of fertilization. The 

 old dried shells found in some fish represent eggs that have been 

 OA'erretained, the egg substance having been resorbed, a process that 

 may be injurious or fatal in its effects. There is also abundant evi- 

 dence that retained eggs retard the maturing of eggs in the next 

 season and cause a diminution in the number produced or even effect 

 a temporary apparent sterility of breeders. It is therefore impor- 

 tant for spawn takers to know just when to expect to find mature 

 eggs in large numbers. The number of eggs yielded by rainbow 

 trout of various sizes was found to vary from about 400 with fish 

 of 10 to 11 inches in length to 2,500 (one instance) with a fish 

 19. 5 inches in length. 



Other observations and experiments at Erwin, Tenn., the re- 

 sults of which can not be given at this time, related to the produc- 

 tion of natural food supply in ponds, the use of a hexagonal tank 

 in place of long hatching troughs, and the effect of the alkalinity 

 of the spring water at Erwin upon the fish that it is attempted to 

 rear in hatching ponds. 



Prof. C. B. Wilson, temporary investigator, has been engaged 

 in completing a study of the role that beetles play in pondfish 

 culture. During the past year the complete life histories of five 

 species of beetles were added to those obtained previously. In 

 addition to this study of the relation of beetles to pond culture 

 Professor Wilson has begim a similar investigation of water bugs. 

 Observations have been made on the life histories of two species of 

 Notonecta, one of Ranatra, and one of Belostoma. Valuable ob- 

 servations on the food and enemies of both nymplis and adults 

 have been recorded. Advantageous and detrimental relationships 

 of beetles to fish have been noted, and methods of control of unde- 

 sirable species have been made available. 



At the instance of the Iowa State Game and Fish Commission an 

 examination of Clear Lake, Iowa, was made by H. L. Canfield, of 

 the fisheries biological station, Fairport, Iowa, with a view to ascer- 

 taining conditions affecting the supply of food and game fishes of 

 the lake and to suggesting possible means of bringing about an in- 

 creased game-fish production. In brief, the recommendations had 

 reference to the development of commercial fishing for capture of 

 rough fish, the artificial propagation of the desired game fishes, and 

 the preservation and protection of areas of shallow water and of 

 vegetation. 



DISEASES AND PARASITES OF FISHES. 



The position of fish pathologist in the bureau was vacant during 

 the greater part of the fiscal year, so that investigations in this field 

 could not be continuously conducted. In February Dr. H. S. Davis, 

 formerly professor of zoology in the University of Florida and at 

 times temporary investigator for the Bureau of Fisheries, assumed 

 the position and devoted his attention in part to the completion of 

 certain studies of the parasites of fishes previously brought near to 



