GAS DISEASE IN FISHES. 369 



EFFECT OF SUPERSATURATED WATER UPON EGGS AND FRY. 



At Woods Hole sea water which was soon fatal to adults or fishes 

 approaching- maturity did not affect eggs and fry. Eggs of the cod were 

 incubated for some two weeks in such water and the fry remained in it 

 until planted — not more than a few da3^s at most, it is true, but a longer 

 period than would suffice to kill adults — 3^et neither were injured or 

 showed any gas sj^mptonis. It is probable, however, that ver}^ young 

 fry are not necessarily immune under all conditions of supersaturation. 

 Bubbles of gas have been noticed in the sacs of shad fr}' at fish cultu- 

 ral stations. Mr. J. N. Wisner (1900) reports such a case at Havre 

 de Grace, Md., and the circumstances point to a leaky suction pipe, 

 liut nothing is known of the degree of supersaturation, if any existed. 

 Theoreticall}^ it seems difficult to avoid the conclusion that oxidation 

 must be attended by an elevation of temperature even in so minute a 

 creature as a newly-hatched cod fry; but this elevation must be infini- 

 tesimal, for the consumption of energy necessary to maintain a tem- 

 perature appreciably above the surrounding water is not supposable 

 in the eggs or fry. As such an elevation of the blood temperature is 

 the chief cause of gas precipitation in adults, its absence in the fry 

 may be taken as strongh'^ tending to explain theii" immunit3\ On the 

 other hand, a sufficiently high degree of excess may be able to cause 

 a separation of gas such as above noted among shad f r}^, either b}^ direct 

 osmosis or via the circulation. 



METHODS OF PREVENTING THE GAS DISEASE. 



The proper aeration of water, by artificial means if not already 

 accomplished by nature, has from the beginning been recognized and 

 insisted upon by tish culturists as of fundamental importance. By 

 aeration was meant the process of putting the water thoroughly in 

 contact with the atmosphere, so that the dissolved air would be increased 

 were there an}' initial lack. In a proper fish-cultural sense, aeration 

 more strictly meant oxygenation, for it was the oxygen alone, the 

 prime necessity of fishes, which was apt to be lacking. No cases, per- 

 haps, are known in which natural waters have less than their proper 

 or normal amount of nitrogen. But of course the aeration process 

 adds both the atmospheric gases should the water be lacking in both. 



The readily observed distress and suffocatiori of fishes by the exhaus- 

 tion of the dissolved oxygen in unrenewed water, the efficacy of even 

 the simplest means of aeration in restoring the life-supporting quality 

 to the water, as well as the generally understood necessity of oxygen 

 to all animals, resulted naturally in an appreciation of the value and 

 necessity of aeration. There were no observed facts from which one 

 would infer the opposite condition in water, an excess of one or more of 

 the air gases, nor were theoretical considerations likely to lead readily 

 to its conjecture. It is improbable that any symptoms or mortality 



F. C. 1904—24 



