Chapt. xvi. The rivers of the Ocean. 219 



water rivers of varying depths and velocity, of greatly 

 varying temperatures, with banks and courses as well 

 defined as fresh water rivers, with counter currents or 

 back sets along those watery banks, some of them flowing 

 on the surface, some at the bottom. From their widely 

 varying circumstances, these vast sea rivers naturally 

 support different sorts of insect life, or in other words dif- 

 ferent sorts of food for fishes.' These currents or sea rivers, 

 their strength, their length, their depth, their, breadth, 

 their course, their temperature, their saltness, have been 

 laboriously ascertained; the mariner has them all well 

 laid down in charts, and studies them carefully. The 

 sea pisciculturist should do likewise. I hold that he can 

 expect to make little progress in his science till he studies 

 it from this point of view. What should we know about 

 the salmon and its propagation if we had always watched 

 it in one particular pool, and not taken into consider- 

 ation the flow of the river, and its varying circumstances 

 in different parts of its course. The same remark applies 

 equally to the Mahseer, which is migratory only in fresh 

 water. Similarly, how can we expect to understand the 

 migrations of herrings, mackerel, pilchard, etc., etc., unless 

 we study them with special reference to their rivers, the 

 salt-water rivers of the sea-. 



Having then floating spawn and flowing rivers in the 

 sea, it is easy to conceive that the former is carried great 

 distances by the latter, and frequently taken out of our 

 ken. But if we identified the sea rivers in which parti- 

 cular spawn was shed, we might, by referring to their 



28* 



