72 U. S. BUREAU OF FISHERIES. 



method of shipping eggs may possibly be more safe than the careful tray method, 

 simply because it confines scratching of the eggs to the outer layers, keeping 

 the inner ones intact. On the trays, however, each egg is carefully placed on 

 <:-loth, which, of course, exposes it to friction with rough places in the latter 

 and also stray bits of pacliing material. Careful statistical scrutiny of ship- 

 ping records should decide this, however, since no reliance can be placed on 

 individual shipments, wherein the amount of rough handling is so exceedingly 

 variable. 



Summary. — (1) Both bacteria and periblastic activity are instrumental in 

 the progress of white spot as it commonly occurs. (2) Neither of these fea- 

 tures can be considered as the primary cause, liowever, since either can occur 

 only in "predisposed " eggs. (3) " Predisposed " eggs are those which have been 

 subject to physical injury of some kind. 



BLUE SAC DISEASE. 



This disease is otherwise known as Hydrocele embryonalis or yolk-sac 

 dropsy. Dr. Bruno Hofer, in his " Handbuch der Fischkrankheiten, " treats 

 of this affection, and in doing so says that many breeders agree that it is 

 probably due to shock or pressure to the eggs, though nothing appears to be 

 certain concerning the etiology. 



The disease appears sporadically, the first symptoms being an enlarged sac, 

 which after a time becomes so weighty that the fry are unable to rise to the 

 surface. After a few days the sac usually bursts, resulting in the death of the 

 fry in a few hours. 



The sac appears to contain a serous fluid, which surrounds the yolk and at 

 times assumes a bluish tinge, hence the name blue sac. The disease seldom 

 appears after the yolk sac has been nearly absorbed but usually attacks the 

 fish during the first week after hatching. 



Hofer seems to think that the disease is caused by rough handling of the 

 <»ggs, whereby they receive shocks or jars or are injured by too much pressure 

 during stripping. He also mentions the probability of the disease being caused 

 by the taking of eggs from brood fish that are too young, and says that pre- 

 caution should be taken against the taking of eggs from very young females; 

 also that care should be exercised in handling and packing for transportation, 

 and that eggs prepared for shipment should be packed in an abundance of soft 

 insulating material, such as moss, etc. 



It has been suggested that improper fertilization may be responsible for the 

 disease. Improper fertilization may not be exactly the correct term, but it is 

 well known that any injury to eggs or sperm will produce monstrosities or 

 diseased offspring. 



Up to this point no definite cause of or remedy for the disease is known, 

 though several possible causes and their prevention have been mentioned. 



L. von Betegh has made a study of the disease. Its sporadic occurrence led 

 him to believe it infectious, and he attempted to isolate the specific organism 

 causing the malady. 



In the serous fluid of the yolk sac he found a diplobacillus in pure culture. 

 This organism he proposed to name Diplobacillus liquefaciens piscium. Von 

 Betegh concluded that the organisip he found may be regarded as the specific 

 cause of the disease. Though he states that further experiments will later 

 be reported on, it does not seem that the mere presence of this diplobacillus is 

 evidence that it causes the disease, yet it is not improbable that it does. 



We must look for all diseases of young fish to arise from one of two causes, 

 namely, infection or injury to the eggs. It is highly probable that this disease 

 may be prevented in a hatchery if the hatching apparatus is kept perfectly 

 clean, all fish suspected of disease are immediately removed and destroyed, 

 and care is exercised in handling the eggs and fish. The stripping of eggs 

 from very young brood stock should also be avoided. 



George A. Seagle, former superintendent of the bureau's Wythe- 

 ville (Va.) hatchery, speaks of the diseases occurring among the 

 rainbow trout at that station, as follows : 



The diseases most frequently occurring among rainbow-trout fry under do- 

 mestication are an inflammation of the gills and a slimy skin alfection. The 

 <;auses of these diseases are not well known, but improper food, water pollu- 

 tion, or insanitary conditions of any kind are among the most probable. By 



