73 



After spawning, the spent fish migrate denatantly as a rule, 

 and many of them enter territorial waters. 



The migrations of the southern race of plaice are similar at 

 maturity, but the direction is towards the English coast or the 

 Channel. It is again a contranatant migration. 



It will not be necessary to review at length the life histories 

 of the remaining species, for it is obvious that with reference 

 to fish with similar habits the sequence of events is bound to be 

 much the same. 



The flounders of the Northumberland coast also come from 

 a spawning ground off the coast of Fife ; other spawning grounds 

 are situated to the north and the south of the Tyne, but these 

 contribute to schools in the North Eastern district. The spawn- 

 ing takes place in March and April, and the recruits appear inshore 

 in June. During the years of immaturity the flounder in spite 

 of its marked predilection for fresh water behaves much as the 

 plaice. It does not migrate from the district, and not for a great 

 distance within the district. Maturity occurs at a size of about 

 25 cm., and the flounders from that size to over 40 cm. migrate, 

 the most of them, to the east coast of Scotland. But as with other 

 species all the adults do not become mature every season. The 

 spent fish may migrate to a great distance denatantly, and are 

 common inshore. 



Amongst the other flat fish, turbot and brill are similar in 

 distribution and habit to the plaice and flounder. 



The dab is different at all stages. Spawning takes place 

 from March to May ; the young appear inshore about June, but 

 they are spread over wide areas of various depths. The inshore 

 dabs are markedly periodic at all events as illustrated by our 

 experiments in regions close to the coast ; their seasonal migra- 

 tions are distinctly related to temperature. At the same time, 

 they exhibit a strong tendency to denatation, even at a size of 

 between 15 and 20 cm. As a result they are distributed along 

 the coast of Northumberland and in the region of the Forth in a 

 manner exactly opposite to the plaice. They predominate in the 

 southern parts of these regions, and tail off to the north. The 

 fact that such a distribution is repeated on the adjacent regions 

 of the east coast of Scotland and Northumberland plainly proves 

 that we have nevertheless to deal with two schools derived from 



