THE LIFE-HISTORIES OF FISHES 159 



together on some particular areas known as spawn- 

 ing banks. Except in the case of the herring, 

 however, there is not evidence in favour of the 

 existence of such definitely localised spawning 

 grounds. It is more likely that the places which 

 depth of water and other conditions constitute 

 suitable habitats are also the spawning areas. If, on 

 a chart such as that of the north-west portion of the 

 Irish Sea, the portions where (say) spawning plaice 

 are fished be marked, it will be found that prac- 

 tically the whole of the sea where the water is 

 about twenty fathoms deep is a spawning area. 

 Hensen, in his North Sea quantitative plankton 

 investigations, found that fish eggs of any one 

 species, such as the cod, plaice, flounder, etc., 

 could not be assigned to any particular places, but 

 were distributed generally over the whole area 

 investigated by him.^ In the case of the herring, 

 however, definite spawning places, such as that on 

 the well-known Ballantrae Bank in the Firth of 

 Clyde, and some other places on. the east coast 

 of Scotland, have been found. There are some 

 exceptions to the general rule that fishes deposit 

 their spawn in deep water off shore. Thus, it is 

 very probable that both flounders and dabs may 

 frequent water near the shore, and of comparatively 

 little depth (five to ten fathoms). 



There are, however, some species of fishes which 

 make very definite spawning migrations. Thus, 



1 Wissenschaftliche Meeresuntersuchungen, Band ii., Heft 2, 1897. 



