616 SCIENCE PROGRESS 



Influence of Physical Conditions on the Metabolism of 



Fishes 



The shoaling movements which lead to the Lofoten cod- 

 fisheries are spawning and not feeding migrations. The fishes 

 do not come into shallow waters (in this particular case) to feed. 

 It is rather the ripening of the reproductive organs which deter- 

 mines the period at which they come to the shore. No doubt 

 this annual spawning migration is a habit which is deeply 

 stamped on the fish by heredity. For some reason or other— 

 probably because the prevalent drift of surface water in this 

 locality leads to a distribution of the pelagic eggs and larvae 

 which is favourable to the species — the adult fishes approach 

 the shallow coastal waters in order to deposit their eggs. But 

 the ripening of the reproductive organs is the immediate 

 stimulus which determines at what precise time the shoaling 

 of the fish takes place. 



Is a late fishery to be associated with a retardation of the 

 annual maturation of the eggs or spermatozoa? It is with 

 regard to such points that the commercial statistics fail, and 

 precise scientific observations become necessary. There is 

 comparatively little in the records of the Lofoten, or, indeed, 

 any other great fishery, which throws light on this point. 

 Systematic and very abundant observations of the progress of 

 the maturation of the gonads in marine edible fishes, also syste- 

 matic quantitative plankton experiments, carried out with the 

 object of ascertaining the relative numbers of eggs and larvae 

 present in the sea during the spawning period, would be 

 necessary for the settlement of this point. Some observations 

 made by Hjort 1 do, however, help us. The cod-fishery at 

 Lofoten was quite abnormal in 1903. Only about 5 per cent, of 

 the total season's catch was made in that year before March 15. 

 Week after week passed without the appearance of the fishes 

 on their usual spawning-grounds, and when they did appear 

 it was seen that their condition was wretched (" ganz elend "). 

 The ovaries were only imperfectly matured, and the size of the 

 ova (the best criterion of the stage of maturity) was as small 

 in March as would have been the case in the December of a 



1 Hjort, Some Results of the International Ocean Researches, published by the 

 Scottish Oceanographical Laboratory, Edinburgh, 1908 (translated from Aars- 

 beretning vedk. Norges Fiskerier for 1907. Bergen). 



