200 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



must be anxious to see some definite scientific experiment 

 carried out which would gauge the extent of the results 

 of artificial hatching in a given area, but such an experi- 

 ment is, from the nature of things, most difficult to devise 

 and to keep free from disturbing elements. It is not 

 difficult, perhaps, to define the conditions of the experi- 

 ment in words, but it is very difficult to carry them out 

 satisfactorily in nature. What is wanted is a fjord 

 or circumscribed sea area of which the fish population is 

 approximately known, or in regard to which, at least, we 

 have reliable statistics extending over a number of years, 

 so that we know what an average catch, under given 

 conditions, ought to consist of. To this area the hatched 

 fry must be added, and the fishing must be regulated, and 

 exact records of both processes kept. The experiment 

 must run for at least five or six years — better ten — so as 

 to allow time for the growth of the fish and to eliminate 

 any possible climatic disturbances during a few of the 

 years. It would be important, as a control experiment, 

 to have a second similar area, close at hand, under similar 

 physical conditions and in which the same amount of 

 fishing is carried on, but to which no fry are added. 



Dr. C. G. Job. Petersen, of the Danish Biological 

 Station, in his last Annual Report (VI., 1897) upon the 

 conditions of plaice population in the Limfjord, expresses 

 his conviction that there is an abundant supply, or in his 

 own word, an " over-population," of young plaice pro- 

 duced naturally in the German sea, and that the difficulty 

 to be met lies, not in a scarcity of fry, but in securing 

 that the young fish, having passed through all the dangers 

 of early life, shall be spared from capture until they have 

 reached the age at which their marketable value is greatest. 

 He recommends, therefore, a system of artificial trans- 

 plantation to suitable grounds, such as some parts of the 



