208 



tain typical lengths, and if snch experiments are kept up 

 for some time an approximation to tlie rate of growth may 

 be arrived at. 



Snch experiments have been carried ont 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* 1mm. 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. Kep. Scottibh Fish. 

 Bd., p. 232, 1898. 



