PROGRESS IN BIOLOGICAL INQUIRIES, 1924 41 



the iodine treatment in May, 1923. In this ease small quantities of 

 iodine AA-ere added to the food, which is believed to be more effective 

 than when added to the water. 



During the year a brief paper describing a method for controlling 

 a disease common among aquarium fishes caused by Ichthyoph- 

 thirius was published (Bureau of Fisheries Document No. 959). 

 This was prepared by H. F. Prytherch, scientific assistant. In this 

 paper the author describes two methods of combating the disease, 

 the first by the use of external applications of aluminum sulphate — 

 a 5 per cent solution for dipping and a 8 per cent solution for brush- 

 ing or rubbing the fish. It also Avas found that the application of 

 a 3 per cent solution applied to the diseased parts of fish infected 

 with Saprolegnia gave excellent results. The second general method 

 descnbed for combating Ichthyophthirius is entirely mechanical 

 and consists in arrangements for disinfection of the tanks and the 

 removal of the parasites after they have left the fish. 



The pathologist has on numerous occasions been called into con- 

 sultation by fish-culturists and various Federal and State organiza- 

 tions regarding the cause of and remedies for unusual mortalities 

 among fishes. 



NEAV METHOD OF OXYGEN DETERMINATION 



In many biological investigations, particularly in field Avork, in- 

 formation concerning the dissoh'ed oxygen content of a water sample 

 is essential. Such knowledge is no less A^aluable to the fish-culturist, 

 since in hatcheries, aquaria, fish cars, and in planting fish the Avel- 

 fare of the specimens is dependent upon a sufficient aeration of the 

 water. Very accurate information on the oxygen content of water 

 can be obtained by analytical methods, but the apparatus is break- 

 able and cumbersome and some knoAvledge of chemistry is necessary 

 for its manipulation; a simple method for this determination with 

 a minimum of apparatus has hitherto been lacking. M. C. James, 

 scientific assistant, has developed a method that promises in some 

 degree to satisfy such requirements. 



PHYSIOLOGY AND NUTRITION OF FISHES 



Experiments to determine the effects of vitamin deficiencA' on 

 fish Avere carried on under the direction of Dr. H. S. Davis at the 

 Fairport (Iowa) station during July and August, 1923. While these 

 experinients were not entirel}- successful, owing to the practical im- 

 possibility of preA-enting the fish from getting small quantities of 

 natural food, the results obtained are of considerable interest. 



In these experiments young carp, buffalofish, bluegill sunfish, 

 and bullheads Avere kept on diets that lacked one or more of the 

 various vitamins. In the case of each species the fish Avere diA^ided 

 into fiA-e lots. One lot, the controls, Avas fed a Avell-balanced diet, 

 rich in A'itamins. A second lot Avas fed a ration that contained no 

 vitamins, while the remaining three lots were giA^en rations that 

 lacked either the A, B. or C A^tamins. 



Of the four species of fish used in the experiments, the carp were 

 found to be most satisfactory, and for this reason only the results 

 obtained with this species are given here. However, ^it should be 



