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AGE (yeors) 



Figure 4. — Lipofuscin in rainbow trout, Salmo gairdneri, as a function of age (n = 21). (A) Total lijxjfuscm in 

 brain; (B) weight-specific (mg wet weight) lipofuscin in brain; (C) total lipofuscin in heart; (D) weight-specific 

 (mg wet weight) lipofuscin in heart; (E) total lipofuscin in liver; (F) weight-specific (mg wet weight) lipofuscin in 

 liver. 



Discussion 



Our results indicate that lipofuscin accumu- 

 lated in the brain of Dover sole with time (Fig. 

 2A). The concentration of lipofuscin increased 

 over a wide range of fish lengths and with esti- 

 mated age of 15 years but did not increase with 

 older fish. Several explanations exist for the lack 

 of change in concentration in older fish: 1) older 

 fish were incorrectly aged; 2) growth of brain 

 tissue masked the actual rate of accumulation; 

 and 3) the rate of accumulation changed during 

 the lifespan of this species due to changes in 

 metabolic activity. Either one or several of these 



factors may cause the lack of lipofuscin accumula- 

 tion in older fish. We consider each of these issues 

 below. 



We do not know the accuracy of the age deter- 

 mination in Dover sole but believe it is unlikely 

 that 3 readers would confuse fish aged 30-40 

 years with those of 20 years. Although future re- 

 search will shed more light on this controversial 

 subject, we think that grossly inaccurate age de- 

 termination is the least likely an explanation. 



A key difference between fishes and other or- 

 ganisms in which lipofuscin accumulation has 

 been clearly documented as a function of chrono- 

 logical age (mammals and invertebrates) is that 



405 



