488 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [4] 



The periodical increase and decrease of nutritive matter in the differ- 

 ent parts of the sea depend on the* degree of warmth and light which, 

 during the changing seasons, they receive from the sun. 



Food and temperature exercise a powerful influence on the develop- 

 ment of the eggs of marine animals. 



The eggs of many invertebrate marine animals develop simultaneously 

 with the eggs of fish which come in large shoals ; the young fish there- 

 fore find numerous microscopic embryos in the same water in which they 

 were hatched. By inhaling this water when breathing they at the same 

 time get the food which is most suitable for them. The water flowing 

 through their gills is in a certain sense their mother's milk. If the water 

 does not contain the food which is absolutely required by the young fish 

 they perish as soon as the nutritive yolk of the egg has been consumed, 

 for on water alone no marine animal can live. 



Though it is therefore an easy matter to develop young salt and fresh 

 water animals from healthy eggs in small vessels, because the eggs con- 

 tain, all the substance which is necessary for such development, it is very 

 difficult to raise the young fry in aquaria, because these but rarely con- 

 tain the necessary food. 



There is no doubt that many young fish and other marine animals do 

 not attain to maturity simply because the water where they were born 

 does not contain a sufficient quantity of suitable food. 



The average quantity of sunlight and warmth, repeating itself from 

 year to year, develops a certain quantity of nutritive matter for the ani- 

 mal life of the sea, and the total mass of mature animals of one part of 

 the sea is as large during every period of development as the quantity of 

 food in that part allows, for during every breeding-period all the animals 

 living together in one region produce a much larger number of eggs than 

 the number of mature animals developed from them. The germinating 

 faculty of all species of animals is greater than their maturing faculty. 



One of the most obvious reasons why the maturing faculty of animals 

 decreases is the destruction of eggs, embryos, and young fry by other 

 species or by larger individuals of the same species. Thus, the Core- 

 gowns lavaretus eats the eggs of its own species; large codfish devour 

 small codfish, and eels fill their stomachs with the spawn of different 

 fish. 



In certain localities man exercises a considerable influence on the' 

 maturing faculty of marine animals. In Greenland the whale (Balmna 

 mysticetus) is at present a very rare animal, because Dutch, Hamburg, 

 British, American, and other whalers have caught old and young whales 

 for centuries. 



In nearly all the fishing villages on the coasts of the Baltic and the 

 North Sea the fishermen complain that the former wealth of fish is dis- 

 appearing. It is unfortunately impossible to ascertain from comparative 

 statistics in how far these complaints are justified ; but there is scarcely 

 a doubt that in most of our coast waters more fish are caught within 



