INTERNATIONAL FISHERY INVESTIGATIONS 595 



in the sea had already attained considerable dimensions. Still 

 there were of course considerable gaps in this body of in- 

 formation, many of which at the present time are far from 

 being filled up. Then much of this knowledge did not 

 go very far towards the solution of the numerous problems 

 which confronted the fishery legislators at the beginning of 

 the 'nineties. Still less was a knowledge of the developmental 

 histories of fishes likely to aid in the establishment of a con- 

 nection between the physical changes in the sea which we 

 have been considering and the migration habits of fishes 

 and other animals. Quite another kind of information was 

 required — that concerning the distribution and abundance of 

 fishes at different times in the year and in different regions 

 of the sea. 



If we consider the life history of one of the better-known 

 marine fishes such as the plaice, we will find it to be some- 

 what as follows : At a certain time in the year the fishes which 

 have attained a certain age and size begin to spawn. Some 

 degree of concentration of the fish on roughly defined 

 spawning areas occurs and emission of the eggs then takes 

 place. These eggs rise to the surface of the sea, drift about 

 there while undergoing development — a process which requires 

 about a fortnight or longer, according to the temperature of 

 the sea. When the larva or young fish hatches out from the 

 egg, it drifts about passively at, or near, the surface of the 

 sea for a certain time until it undergoes the metamorphosis 

 through which it passes into the juvenescent stage in its life 

 history. It then seeks the shallow waters on the sandy coasts 

 and there it remains for the next two years of its life, feeding 

 and growing rapidly. Then begins the migration into the 

 deeper parts of the sea, during which the fish is assuming 

 the adolescent stage and the reproductive organs are arriving 

 at their phase of maturity. In the fourth or fifth year of life 

 the plaice has attained sexual maturity and begins to produce 

 ripe eggs. 



Such a life history, though applying precisely to the plaice, 

 is also characteristic of many other marine fishes. Generally 

 speaking, we can divide fishes into two main groups, one of 

 which, the demersal or bottom-living fishes, have a life history 

 which in its broad outlines resembles that indicated above. 

 There is also a less numerous group of fishes with a life history 



