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DISCUSSION 



Rockstein: Which is the longest-Uved freshwater fish known? 



Nigrelli: In captivity it is this sturgeon which hved 69 years. 



Beverton: Sturgeons are also the longest-lived according to field 

 observations; the longest we have ever seen recorded was 151 years, 

 an estimate based on the number of rings in the rays of the pectoral 

 fin. Are any age determinations of the conventional kinds done on 

 these fish at death? 



Nigrelli: We have attempted to make age determinations but we 

 have given it up as hopeless because at these steady temperatures 

 they lose the markings. We do take measurements of the fish though, 

 to give us some idea of growth. 



Scheidegger : In which organs have you found cancer? 



Nigrelli: In practically every organ. We have also seen virus 

 tumours, and I have published a paper (Nigrelli, 1952) on virus in 

 relation to cancer. There are two or three interesting "tumours", 

 however, that are not of the neoplastic type, and one is well known in 

 Europe — it is called lymphocystis disease (Nigrelli, 1954a). It was 

 first described in English plaice but it is widely distributed both in 

 freshwater and marine species. This is a hypertrophy of the con- 

 nective tissue cells in which diseased cells blow up from about 10 fx to 

 • 5 mm. or more. This disease was definitely shown to be of virus 

 origin. 



Holt: Most of the long-lived species are rather large, but there are 

 clear exceptions, just as there are for mammals, where rats and bats 

 of roughly the same size, as Mr. Sacher pointed out, have quite 



