[55] FISH CULTURE IN CENTRAL EUROPE. 593 



eggs of salinonoids are usually shipped. An important condition for 

 raising carp is that the ponds can be laid entirely dry. 



The rules to be observed in artificial fish-culture are, however, much 

 more numerous. According to Benecke they may be classed under the 

 following categories : Obtaining and fecundating the eggs in an artifi- 

 cial manner, hatching them, raising the young fish until they have lost 

 their umbilical sac, shipping them, and placing them in suitable 

 waters. 



The artificial fecundation of fish eggs is, at present, generally prac- 

 ticed according to the dry method, the Russian method of Wraskij. By 

 a gentle pressure on the abdomen the mature eggs are extracted from 

 the body of the female, and allowed to drop into a dry vessel ; over the 

 eggs is poured the seminal liquid obtained in the same manner from 

 the male ; the mixture is gently stirred with the hand, gradually adding 

 a little water. Eggs have even been successfully fecundated which 

 had been taken from female fish which had been dead several hours. 



The best fish for propagators are those which are not too old; this ap- 

 plies particularly to the male fish. It is advisable not to use the same 

 fish as propagators for several years in succession, with the view to 

 avoid the evil consequences of the fatty degeneration of the genital 

 organs, advanced age, and consanguinity. If the fish selected for the 

 purpose of reproduction are healthy and fine; their products will be so 

 likewise. It is possible to produce hybrids; but these, besides being 

 barren, show a very high rate of mortality, and in my opinion their 

 raising can not be recommended. 



The eggs, after having become fecundated, are subjected to the 

 hatching process. In a temperate climate this process may be effected 

 in the open air and in open waters, in apparatus either floating or 

 placed on the bottom of a brook or some other water-course; but it is 

 always safer, and in most cases absolutely necessary, that the hatching 

 should be done in covered and inclosed places, which are called hatch- 

 ing-houses. These should be constructed in such a manner that the 

 water inside is not liable to freeze ; they should have sufficient light, 

 so that there is no difficulty in selecting the eggs; but the light should 

 not be too strong, because this favors the development of algae and 

 parasitical fungi. 



The principal question which should engage the attention of fish-cult- 

 urists, is the selection of the water destined for the hatching-house. It 

 should be clear, free from impurities, have a low and even temperature 

 (possibly from 2° to 5° C. [35.6° to 41° P.]), and, what is still more im- 

 portant, should be abundantly aerated. These conditions are found 

 particularly in brook water, which has only one fault, namely, that it is 

 frequently muddy. Spring water is generally too warm and too little 

 aerated, but both these defects may be remedied by letting it, before 

 entering the hatching-house, run for some distance through a covered 

 canal over a bed of gravel, and forming some little falls. Wherever 

 S. Mis. 90 38 



