THE FISHERY INTERESTS OF AUSTRIA. 581 



proved astonishingly successful, would immediately tend to restock all 

 our lakes and rivers. 



The law of nature by which fish are increased by the enormous fruit- 

 fulness of a single pair is counterbalanced by another law of nature, 

 which permits the destruction of equally large numbers of fish during their 

 period of development, thus restoring the proper balance in the house- 

 hold of nature. Hitherto, man has only disturbed this balance, and no 

 endeavors were made to counteract destruction by taking measures for 

 preservation and increase. 



On the continent of Europe, many races of animals that were hostile 

 to man, or at least useless, have, by this continued war of destruction, 

 either been entirely annihilated or very much diminished, in numbers ; 

 those, however, whose preservation and propagation are protected by 

 human laws and customs, those which have enjoyed the care of man, 

 have not only been preserved and increased, but also considerably im- 

 proved. Just as man in the care of his domestic animals does not leave 

 everything to nature alone, but rears them on practical and scientific 

 principles, he must also carry on fish-breeding in a similar manner. 



It is the object of artificial pisciculture to make use of the spawn 

 which nature provides in rich profusion, and to protect it against all 

 hurtful influences in nature, as well as to provide the fish in a plentiful 

 manner with the food which they require for their development. 



Of the enormous number of fish-eggs, a large portion is never fertil- 

 ized, the cause of this being the peculiar manner of impregnation, 

 which takes place outside of the body, as the female lets the eggs 

 (roe) drop into the water, and the male pours the semen (milt) over 

 them. The eggs of most species of fish lie free on the bottom, only cov- 

 ered a little by pebbles and sand, or are by some, as is the case with 

 the perch; pasted on aquatic plants and stones. During the breeding- 

 season, which lasts several weeks, the eggs are exposed to numberless 

 enemies. Wherever the spawning places have not been properly pre- 

 pared, many of the eggs are either washed away by the water, or thrown 

 on the dry land by the waves, or scattered by removing the plants or 

 the sand. Some fish, which are in the habit of gliding along the bottom, 

 such as the turbot, the groundling, and likewise the perch, feed almost 

 entirely on fish-eggs during the spawning-season. No less hurtful are 

 the numberless lar of insects, diminutive crabs, water-mice ? and all 

 aquatic birds, such as ducks, geese, &c. The vegetable kingdom also 

 contains many enemies of the fish-eggs, such as the small plants of 

 which mold is composed, whose germs sticking to the outer skin of the 

 egg, soon commence to sprout forth, and destroy enormous quantities of 

 them. The eggs of those fish which spawn in winter, among which 

 there are some of the finest species, are frequently exposed to the dan- 

 ger of freezing to death. The young fish during the period when they 

 lie helpless at the bottom, and receive their food from the umbilical bag, 

 are threatened by numberless enemies such as fish of prey, insects 



