V GROWTH, MIGRATIONS, FOOD AND HABITS 109 



it from an immature roe. The plaice and certain other fishes are 

 rapid spawners, and therefore shotten fish begin to be seen early 

 in the spawning season, and may be confused with immature 

 before the end of it. In the sole and other species which spawn 

 slowly there is little danger of confusion if the examination be 

 made in the earlier part of the spawning season. 



At Grimsby it was found that the smallest mature females, of 

 plaice caught in the northern part of the North Sea, were 13 

 inches long, the largest immature not quite 18 inches. Of males 

 the smallest mature were 9 inches long with the exception of 

 one at 6 inches, and the largest immature not quite 16 inches. 

 At Plymouth the corresponding limits were 9 inches and 15 

 inches for female plaice, 9 inches and 12 inches for males. It is 

 thus evident that the plaice in the western part of the Channel 

 attain to maturity at a smaller size than in the North Sea, and 

 the fact that the average or usual sizes in the Channel are also 

 smaller indicates that the cause of the difference is not an earlier 

 or precocious maturity, but a permanent inferiority in size. It 

 has been shown that the smaller or Channel race of plaice 

 extends northwards from the Straits of Dover along the Dutch 

 coast, a considerable proportion of mature specimens being 

 found between 9 and 14 inches among the plaice caught on the 

 Brown Ridges, from thirty to fifty miles off the Dutch coast a 

 little to the south of the Texel. On the other hand the small 

 plaice taken on the Continental coasts in the neighbourhood of 

 Heligoland do not belong to the smaller race, none of the females 

 being mature below the length of 1 3 inches. 



The smallest mature female sole is loi inches, the largest 

 immature 12 inches, the average 11 inches ; the average for the 

 males being 9 or 10 inches. The haddock begins to spawn at 

 II to 16 inches in the female sex, 11 inches in the male. The 

 size of the cod at maturity is of course greater, namely, 22 to 35 

 inches in both sexes. It is unnecessary to give further particulars 

 here, they will be found in the separate histories of the different 

 species. 



We have seen that the immature fish may be a year old, we 

 have now to consider whether some individuals spawn w^hen 

 only one year while others are immature, or whether all or only 

 some spawn at two years. In the case of some fishes whose 

 movements are restricted, which live in estuaries or rivers, it is 



