Discussion 227 



different lifespans. We find the exceptions among the large fish in 

 that sturgeons and tunas of about the same size have quite different 

 growth rates and lifespans, but I do not know any examples of very 

 small fish which are long-lived. None of those indicated as reaching 

 20 years or more were small species. By small fish I mean those with 

 low upper limits to Lqq. Are there some such fish which commonly 

 live for ten years or more? 



Comfort: There is a reported instance of a goldfish being kept till 

 40, but it was small and had been kept in a barrel. (Hervey, G. F., 

 and Hems, J. (1948). The Goldfish. London: Batchworth Press.) 



NigrelU: That is an important factor in aquarium management. 

 Fish are restricted in size by the size of the container, though not 

 necessarily by the volume of water. Tarpon have been kept, for 

 instance, for seven or eight years, and some have never grown larger 

 than about 18 inches. An 8-year-old tarpon in the wild might be 

 about 4 feet long or more. 



Holt: By small fish, I did not mean fish which were artificially 

 kept small, but ones which cannot grow big no matter how much 

 food or space they are given. 



NigrelU: There are several examples of small fish, hke goldfish, 

 that live for about ten years (see Table III). 



Comfort: The matter of fatty degeneration is one which has 

 always puzzled me when looking at pathological sections. The 

 normal liver, in the guppy at any rate, looks very fatty but I do not 

 know if it is degenerate. In underfed fish the liver is much more 

 cellular. 



NigrelU: Glycogen infiltration is also evident in stained sections. 



Comfort: I suspect that a lot of what appears to be degeneration 

 is reversible, and is actually fat storage. 



NigrelU: We call it fatty change and it does indicate a disturb- 

 ance of lipid metabolism that is not reversible. 



Comfort: I believe you showed that fatty degeneration occurs in 

 small aquarium fish fed only with enchytrae and nothing else? 



NigrelU: That is correct. 



Bourliere: It is interesting to notice that tuna are said to have a 

 higher internal temperature than most of the other marine fish of 

 similar size. Maybe there is here again a correlation between 

 metabolic rate, growth rate and ageing rate. 



Has any study ever been made on the relative incidence of the 

 various pathological causes of death in wild fish? 



Beverton: I do not know of any comprehensive study. A member 

 of the Aberdeen Fisheries Laboratory has taken it up as his special 

 subject in the last year or so. 



