AETIFICIAL PROPAGATION OF TEOUT. 69 



Remedial measures. — No cure for this disease has yet been found. Exter- 

 nal application of some solution is indicated. Salt solutions are not efficacious; 

 thorough sanitation may be of assistance. Diseased fish should bp isolated 

 or destroyed ; infected troughs and implements sterilized. Experiments with 

 curative measures are in progress. 



At the Neosho (Mo.) station of the bureau a 1 to 15 sohition 

 (approximate!}^) of cider vinegar has been found effective in treat- 

 ing this trouble. The sohition is prepared in a tub or any suitable 

 vessel; the affected fish are removed from the trough with a dip net, 

 immersed in the solution for a period not to exceed 8 to 10 seconds, 

 and are returned immediately to fresh running water. The fish 

 should be watched closely while in the solution and not retained in it 

 beyond the point where they manifest undue distress by turning on 

 their sides. Because of the variation in the strength of cider vine- 

 gar a 1 to 15 solution will not always give the best result. It woidd 

 be well, therefore, for the practical fish-culturist to note the effect 

 of his solution on a limited nimiber of fish before treating the en- 

 tire lot. 



Tl-out eggs and fry, as well as fingerling and adult trout, are sub- 

 ject to disease. Perhaps the more common affections are the so- 

 called " white spot disease " and the " blue sac," some notes on which 

 are appended. The discussion pertaining to the white spot disease 

 is quoted from a report on the subject by Dr. Franz Schrader, while 

 the discussion of the blue sac is taken from a memorandum by Dr» 

 Adrian Thomas. 



WHITE SPOT DISEASE. 



This trouble manifests itself by the appearance of an opaque or white area 

 in some part of the embryo, very generally the yolk. There the gradually 

 expanding milky white area is very noticeable in its semitransparent sur- 

 roundings, and the affected eggs are easily recognized, even in the early stages 

 of the disease. Any stage of development up to the complete absorption of 

 the yolk sac may show the infection, and its appearance has come to be 

 recognized as certain death to the affected specimen. Although by no means 

 confined to the eggs, it is in the eggs of salmonoid fishes that it is most con- 

 spicuous and most easily observed. 



The hjTDOtheses of fish-culturists as to the cause or causes of white spot 

 are more or less indefinite. Weakness of the parent fish, water temperatures, 

 rough handling, holding of the adult fish under unfavorable conditions during 

 the spawn-taking period, are some of the more common causes ascribed. In 

 connection with the last one mentioned the belief is held by some experienced 

 fish-culturists that the transfer of spawning fish from one pond to another 

 just prior to the spawning period may be conducive to white spot, and that 

 such contemplated transfers of adult fish should be made well in advance 

 of spawning or not until after that function has been accomplished. 



More serious attempts to clear up the nature of the white spot were made 

 by Bataillon (1894) and Hofer (1892). The former was concerned with what 

 was apparently an epidemic of the disease and obtained pure cultures of sev- 

 eral bacteria from the dying eggs, one of which proved patliogenic from cold- 

 blooded animals. Hofer also attributed the disease to bacterial agency, al- 

 though he was unable to obtain pure cultures and found Bataillon's account 

 too indefinite to render a comparison of the organisms concerned of much use. 

 He was inclined, however, to believe that infection occurred through the agency 

 of unclean packing material or the water from contaminated ice, since he ob- 

 served disease only in eggs that had undergone shipment. Shipment might 

 also weaken the eggs so that they would be more susceptible to bacterial in- 

 vasion than untransported ova. According to him both single isolated eggs, 

 as well as the entire contents of hatching troughs, may be affected. 



It must be recognized at tlie outset that any disturbance that will cause a 

 refraction of light at any location in the homogeneous transparant yolk will 



