914 BULLETIN OF THE BUREAU OF FISHERIES. 



in the water close to the fry. The Httle heads at once turn toward the current, 

 the bodies righting themselves upon the yolk sac, and this equilibrium is main- 

 tained so long as the current continues. When it fails the fry fall back on 

 their sides. 



It is suitable currents that also make it possible to feed the very small fry 

 without danger of disease. Even before the yolk sac has begun to diminish 

 they will face the currents and make efforts to catch small particles of food 

 passing some three or four centimeters above them. I have shown this very 

 interesting and amusing sight in aquaria, and it is because of such experiments 

 that I insist the fry shall be fed when four days old. At the end of ten or twelve 

 days, in water having a temperature of about io°, will be observed the occur- 

 rence above noted, and a few days later these fry, developed and strengthened 

 by the food they have had, but still with their yolk sac, may be seen swimming 

 progressively. The fry should not be kept in darkness. They must be able to 

 see their food to get it. 



CURATIVE MEASURES. 



With the precautions I have enumerated the fry will not be affected with 

 the gill disease. If, however, I should find myself confronted with it I would 

 reduce the number of fry by half; I would place them in semiobscurity and 

 would give them no food for several days, in order not to put into the water 

 the slightest substance for putrefaction, and keep the gills free of any organic 

 matter due to the food or its remains. I would have well-aerated water and 

 take care not to leave any dead fish in the troughs. Such would be the treat- 

 ment to be given — a thorough cleaning from the beginning of the disease. But 

 I do not guarantee that I could save fry which were seriously affected. 



The gills are very sensitive to the disease, and their impregnation with 

 organic matter, be it only a temporary one, causes death. I have been a 

 professional fisherman, and all fishermen know very well that fishes caught 

 during the first days of rising water never live, can not live, even if they are 

 taken with the most inoffensive of fishing devices, and this is so because their 

 gills are filled with organic matter and sediment which rising water always 

 carries along. Three or four days after the beginning of the rise of water the 

 gills are slowly cleaned and the fishes live. 



AN EPIDEMIC OF "STAGGERS" IN RAINBOW TROUT FRY. 



The brood trout in this case weighed about four ounces and laid eggs now 

 for the second time. The eggs were placed in filtered spring water at a tem- 

 perature of 9°, io°, and even ii°, and incubation lasted forty days. The 

 greatest hatch took place on March 14, 1906, lasting two days. The small 

 fry were placed in nonfiltered water, where they were kept from March 16 to 

 April 14. 



