American Fisheries Society 373 



There is here a rather curious biological paradox. The 

 thickening of the gill filament is, of course, for the purpose 

 of protection. If it is exposed, its very thin, delicate na- 

 ture renders it liable to injury. The thickening of the gill 

 is a remedial process to relieve that danger, but that very 

 process at the same time must necessarily interfere with 

 the purpose of the gill filament in absorbing oxygen. In 

 other words, this process of nature which preserves the gill 

 filament as a whole at the same time renders it less effective 

 as a means of absorbing oxygen. 



I have not been able, as yet, to find out just what effect 

 these thickened filaments have on the fishes. It may be 

 that some compensatory hypertrophy of the gill lamellae 

 occurs in protected regions of the gill to render such fishes 

 as efficient as normal ones in oxygen absorption. But there 

 is no doubt that if the fishes were in their natural environ- 

 ment, such exposed gills would render them much more 

 liable to the attack of parasites in the gill region, and per- 

 haps to the attack of some other enemies as well. 



I hope to be able to carry this investigation further, and, 

 if possible, to learn what produces this abnormal condition. 

 I suspect that crowding of the young fry may be responsible 

 for it, because in the small hatchery of the Aquarium the fry 

 often do not have sufficient space. The condition is ob- 

 servable very early — in fact, almost as soon as the fishes are 

 hatched out and begin to lie crowded together in our hatch- 

 ing tanks. I know that the same thing also occurs in some 

 of the commercial hatcheries, and that there is a great 

 amount of variation in the percentage of abnormality in 

 various hatcheries. 



I have never observed a single fish developed under natu- 

 ral environment, — and I think I have seined millions of 

 them myself — with this condition. Perhaps some of you may 

 have observed them in your work on wild fishes. I would 

 be very glad to have any suggestions or information that 

 you may have to give on the subject. I hope, as I have 

 said, to be able to discover the reason for this; and if we 



