56 



THE SEA FISHERIES 



lemon sole). The following tables give the total quantity and value 

 of these five species landed in the British Isles in 1913 : — 



It is seen that both as regards quantity and value the plaice is 

 the most important member of the genus Pleuronectes. 



The plaice may be recognised by the following characters :^ 

 Eyes on the right side, mouth at the end of the snout, teeth most 

 developed on the blind side, scales small and embedded in the skin, 

 bony knobs on the head between the eyes and red spots on the 

 upper side of the body. The plaice grows up to a length of about 

 33 in. ; the sizes usually met with in commercial fishing are referred 

 to below. According to Holt the female plaice spawns in the North 

 Sea at an average length of 17 in. ; in the English Channel, Cun- 

 ningham found nearly all plaice were mature at 15 in. 



On the other hand, in Danish waters spawning female plaice have 

 been taken at a length of only 7 in. As a rule the male attains 

 sexual maturity at a lesser size than the female, and in the North 

 Sea ripe male plaice have been captured which were 9 in. in length. 

 In the northern part of the North Sea the average size at which 

 the plaice first becomes mature is for the female I5| in. and for the 

 male 12-^ in. According to Petersen^ the average size in Danish 

 waters is much less than this. Plaice first become mature in the 

 Baltic at an average size of 10 in., in the Lesser Belt at 11 in. and 

 in the Kattegat at from 12 to 13 in. _ 



Probably the plaice spawns annually after sexual maturity is 



1 For a detailed account of the structure of the plaice see Lancashire Sea Fisheries 

 Laboratory Report for 1901. Appendix. " Memoir on the Plaice," \>y^. J. Cole and 

 J. Johnstone. 



2 Fourth Report Danish Biol. Station, 1894, p. 3. 



