American Fisheries Society. 193 



any length of time. If a well covered individual were taken 

 from the water for a few seconds all the bubbles would dissipat'i 

 in the air. After the return to the water the fish in a few 

 minutes would be as well covered as before. The blisters in the 

 skin, or on the fins, were not formed until after hours or days, 

 and were of course more permanent, being surrounded by a thin 

 membrane — a layer of the skin — and really within the fish itself. 

 With some specimens the buoyant effect of the bubbles and the 

 blisters together was plainly seen in the constant effort to swim 

 down in order to keep below the surface. The evolution of gas 

 bubbles was not confined to the fishes alone, but appeared upon 

 the sides of the aquarium tanks and on nearly any mechanical 

 surface submerged in the water. 



It should be said that at other seasons, chiefly in the summer, 

 "popeye" was common among the fishes, the scup being particu- 

 larly affected. At the time of the occurrence of the mortality of 

 the past winter the scup was not in season and the species then 

 used in the aquaria did not exhibit popeye. While it is at least 

 possible that this bulging of the eyes is due to the same cause as 

 the gas symptoms here described, the popeye of the scup and 

 other summer species is not necessarily included here. There is 

 undoubtedly more than one kind of popeye. 



These fishes soon died, after varying periods, some in a fev/ 

 houis, others living several days. Aside from the symptoms of 

 gas already mentioned they showed but little external evidence 

 of disease or injury. On opening them, however, a strange and 

 unusual condition appeared. Gas was present in the larger 

 blood vessels. The heart itself contained gas as well as blood, 

 and was sometimes found with one of its chambers distended 

 with gas to the exclusion of the blood. The vessel from th-3 

 heart to the gills could be traced empty of blood, and the gill- 

 filaments had each a plug of gas which plainly made the pas- 

 sage of blood impossible. In these cases the cause of death could 

 be plainly due to suffocation. In some way gas had been liber- 

 ated within the blood vessels and finally accumulated in such 

 amounts as to entirely obstruct the circulation. The external gas 

 alreadv described evidently did no particular harm, but thah 

 within the blood vessels was fatal, as it is within the human ves- 

 sels when present in any considerable amount. 



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