274 BRITISH FISHERIES 



2. The larval phase, which lasts from the end 

 of the embryonic period until the time when the 

 " metamorphosis " has been completed ; 



3. The period of juvenescence, lasting until the 

 reproductive organs have been matured ; and 



4. The period of sexual maturity. 



In most cases the limits of all these phases have 

 been determined. Thus, the embryonic period of 

 the plaice is about 14 to 1 8 days ; the larval 

 period lasts from the time of hatching until the 

 little fish is about six weeks old ; and the con- 

 dition of sexual maturity is only attained during 

 the third or fourth year, when the fish has reached 

 an average length of about 1 5 inches. Turbot be- 

 come mature when they are about 1 8 inches long, 

 brill at about 15 inches, soles at about 12, cod 

 about 30, haddock about 12, and whiting about 9. 

 But these sizes at sexual maturity vary within rather 

 wide limits : thus, mature plaice are smaller in 

 Danish waters (the Cattegat, for instance) than in 

 the English Channel, and smaller again in the 

 latter area than in some parts of the North 

 Sea. Local conditions will influence the sizes 

 at which sexual maturity is attained to a very 

 considerable extent, and the determination of the 

 latter must be carried out for each particular 

 locality. 1 



1 See Fulton, Report, Scottish Fishery Board for 1889, part iii. 

 p. 157, for the first attempt at the determination of the spawning sizes 

 of fishes. 



