174 R. J. H. Beverton and S. J. Holt 



of the question as to whether ageing in fish differs funda- 

 mentally from that in higher vertebrates. A more profitable 

 approach would seem to lie in a better understanding of the 

 intrinsic causes of natural death in fish, about which relatively 

 little is yet known. A recent study of the European eel 

 {Anguilla anguilla) by Tucker (1959) suggests that the debility 

 of these fish at the inception of gonadal and other hormone 

 activity, which causes them to drift passively downstream, is 

 due to demineralization of the starving body. That this 

 process is reversible, at least in the early stages, is shown by 

 the fact that silver eels imprisoned in fresh water can survive 

 by regression of the gonads and consequent remineralization 

 of the body fluids ; and it is also known that recovery of the 

 Atlantic salmon (Salmo solar) after spawning can be hastened 

 by placing them in salt water. It is true that both these 

 species, and more especially the eel, have a highly atypical 

 life history, but this kind of explanation of certain behavioural 

 patterns in physiological terms would appear to be an essen- 

 tial step in the solution of at least some aspects of the problem 

 of longevity in fish. The other line of investigation that would 

 seem to be of special significance is a comparative study of the 

 physiology of growth and reproduction in species which have 

 a post-reproductive phase. We would hope that an under- 

 standing of the beginning of the reproductive phase of the 

 life history in relation to growth processes would help inter- 

 pretation of those events at the end of the reproductive life- 

 span that lead to death. 



REFERENCES 



Aasen, O. (1952). Fiskeridir. Skr. Havundersok., 10, (2). 



Akyuz, E. (1959). Unpublished data, filed at FAO, Rome, and Et ve 



Balik Kurumu, Istanbul. 

 Alm, G. (1946). Rep. Inst. Freshw. Res. Drottning., 25. 

 Alm, G. (1952). Rep. Inst. Freshw. Res. Drottning., 33, 17. 

 d'ANCONA, U. (1937). Rapp. Comm. int. Mer Medit., 10, 162. 

 Anonymous (1954). Comm. Fish. Rev., 16, 28. 



Appelget, J., and Smith, L. L. (1951). Trans. Amer. Fish. Soc., 80, 119. 

 Arora, H. L. (1951). Calif. Fish Game, 37, 3. 



