208 
tain typical lengths, and if such experiments are kept up 
for some time an approximation to the rate of growth may 
be arrived at. 
Such experiments have been carried out both in this 
country and in Denmark. Dannevig* found that on the 
East Coast of Scotland the Plaice grows about three 
inches in the year. The average size at the end of the 
first year is 77°2mm., at the end of the second 156°7, and 
at the end of the third year 233'lmm. The experiments 
also show that it is during the warmer part of the year— 
May to October—that growth takes place. During the 
winter it is practically arrested. 
The period following the metamorphosis of the fish 
till the third or fourth year may be called the immature 
stage. It is characterised by the undeveloped condition 
of the reproductive organs, and by the gradual outward 
migration of the fish towards deep water. The ovaries 
remain small and contain only small transparent ova. 
At a variable size and age sexual maturity is indicated by 
the gradual enlargement of the ovaries and testes and by 
the occurrence in the former of eggs containing yolk. 
After the first sexual maturity occurs the ovaries never 
revert to their condition prior to maturity, and it is always 
possible to distinguish a fish which has previously spawned. 
Sexual maturity.—The size at which first-sexual 
maturity occurs is variable within somewhat wide limits 
in the seas round the British Isles, and as a knowledge of 
this size is of considerable importance as a basis for 
fisheries legislation, great pains have been taken to esti- 
mate it for various localities. It may vary within very 
wide limits—thus in Danish waters spawning female 
Plaice of 7” in length have been exceptionally taken, 
* On the rate of growth of the Plaice. 17th An. Rep. Scottish Fish. 
Bd., p. 232, 1898. 
