25 
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. Joh. 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 ‘ of young plaice pro- 
’ 
‘over-population,’ 
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 1s greatest. 
He recommends, therefore, a system of artificial trans- 
plantation to suitable grounds, such as some parts of the 
