INTRODUCTORY 



It 



Lt is only of recent years that attempts have been made to increase or maintain 

 the fish supply in the sea by means of artificial hatching of sea fish. The first experiments 

 were undertaken in America in 1867, while in Europe all hatching of sea fish is of a 

 later date. 



All these hatching operations were instituted at a time, when our knowledge of 

 the natural history of the ocean and fishes was primitive compared to that of the 

 present day. They were founded on ideas then current as to the ocean and the life 

 of the fishes and on hypotheses then in vogue with regard to the economy of the fishes 

 and fisheries. 



The hatching operations seem nowhere to have been based on previous experiments 

 which could clearly illustrate or prove the practical use of these attempts. In Europe 

 at all events the employment of hatching seems rather to have been considered as an 

 experiment with regard to its own feasibility. Clear and precise ideas as to the means 

 at hand for judging the results of this experiment seem however to have been lacking. 

 Really the hatching experiments have offered no safe means of answering the question 

 whether they did any good or not. Irrefutable experimental proofs have nowhere been 

 produced, and as a consequence the utility of sea fish hatching remains an open question. 



An analysis of the chief difficulties in the hatching problem will be easier to 

 understand, if we briefly consider the artificial hatching now in vogue in the culture of 

 fresh water fishes. 



The importance attached to the culture of fresh water fishes and the extent to 

 which it was prosecuted in the latter end of the last century, especially on the European 

 continent, is so well known, that a more detailed review is unnecessary. A summary 

 of our present knowledge of this culture especially the pond-culture (die Teichwirthschaft) 

 will show that it mainly depends on the following: 



1) The production of the species is wholly regulated by man and is realised by means 

 of artificially hatched and reared fry. 



2) The numbers and sizes of young fish added to the water in question are exactly 

 determined by experience of the numbers and sizes, which the water is able to 

 nourish during a certain time, until the most advantageous marketable size has 

 been reached. 



3) All competition between different year classes of the same species is excluded. The 

 water must contain only one species. 



4) The water must be of a size permitting every fish to be easily caught at any moment. 



