30 FISHERY AND FUR INDUSTRIES OF ALASKA IN 1912. 



shade of doubt regarding the scale rings of spawning fish, but in no 

 case can these fish be adjudged to be more than 5 years old, and they 

 are in all probability only 4 years old. In the case of two examples 

 of complete loss of ventrals, a rough dissection indicated that the 

 pelvic arch had been wholly lost. This tends to prove that the 

 removal of the fins occurred at a very early age. In an example with 

 one fin partially removed, leaving only a stub, there had been no 

 atrophy of the arch. 



The suggestion that these fish are of the lot marked in 1903 is 

 absurd. Aside from the inherent improbability of a second group 

 appearing in this way at such a distant interval from the first return 

 in 1906, the record of the scales is final evidence of the real age of the 

 fish. To account for the presence of the fish, there seem to be but 

 two possible h3rpotheses. First, that the disappearance of the fins 

 is due to some natural cause and theu* loss is either congenital or 

 arises from some action of an external agent, such as fungus, upon the 

 fry; or second, that the fish were marked by human agency. 



As against the first proposition is the fact that in all of the exam- 

 ples seen, no fins other than the ventrals are damaged. It is well 

 known that fungus attacks the unpaired fins more often than the 

 paired. The return of about 50 adults would imply that the cause 

 was directed toward some 3,000 fry. The hypothesis that nature 

 suddenly and irregularly produced this many monstrosities is unten- 

 able on its face. Hence, we must fall back on the new factors in- 

 troduced by artificial propagation. The diseases of fry are not 

 sufficiently well known to suggest any affection that would show in 

 the adult in no other respect than m an absence of these fins. Any 

 disorder of the ventral region involving these parts would almost 

 necessarily involve adjacent structures. The only reasonable conclu- 

 sion seems to be that some cause carried away the external fin structure 

 in such early life that the bony arch never developed; that is, atro- 

 phied from a lack of use. For example, it is inconceivable that 

 fungus attacking the fish while in the yolk stage and resting on the 

 bottom could destroy these fins and yet reach no other structure. 

 The only possible proposition that can serve as a basis for argument 

 against this conclusion is that the fungus may have likewise dam- 

 aged the adjacent fins, as the anal, but that these later regenerated 

 while the ventrals did not. Since these "marked" fish were noted 

 only at the hatcheries at Loring and Yes Bay they probably origi- 

 nated in that section. 



Experiments in excising the fins indicate that if the rays are not 

 entirely removed the fin will regenerate, at least partially. It has, 

 as yet, not been determined that the fin wiQ assume its original size, 

 but from the growth observed there is no reason to doubt that it 

 will. The entire removal of any fin or its rays to the base — that is. 



