[9] RAISING CARP AND OTHER POND FISH. 1141« 



aquatic birds and aiuiiials will likewise diminish the produotious of the 

 spawning- ponds. It is therefore necessary to fight these enemies ener- 

 getically and persistently. In my Fish-Culture {Fischzucht) and my 

 Manual of Fisheries and Fish-Oulture (Lehrbuch der Fischerei und 

 Fischzucht), which will be published during the coming summer, I 

 have treated all these subjects at considerable length, and would, there- 

 fore, refer the reader to these works. 



APPENDIX. 



In several respects it is of great importance that ponds should lie 

 dry as long as possible, and that the draining should be thorough. 



It causes the spawning carp to spawn immediately ; the principal 

 cause of this may be that the soil is more thoroughly heated by the 

 sun when it is quite dry. At Berneuchen the water in ponds treated 

 in this manner had in the middle of May a temperature of -f- 16° R., 

 whilst in ponds which had been filled with water for a longer time the 

 temperature was only + 14P E. In consequence of this circumstance 

 the carp spawned at once in the first-mentioned ponds, and produced an 

 extraordinary quantity of fry, while in the other ponds they had not 

 yet spawned on the 2pth June. 



If the ponds are allowed to lie dry, the increase of small crustaceans, 

 on which the young fish principally feed, is greatly favored. All the 

 ponds which I treated in this manner in a very short time literally 

 swarmed with small crustaceans. Professor Benecke, of Konigsberg, 

 had the kindness to examine them, and found principally Daphnia 

 7nucronata, and, in smaller quantities, Daphnia hyalina and Polyphemus 

 oculus. To explain the phenomenon I quote the following from Bronn 

 ^'- Klassenund Ordnungen des Thierreichs^^ — Classes and Orders of the 

 Animal Kingdom — (Vol. V, part 1, p. 955 ) : " The eggs of many branchi- 

 opods, especially those of the Gladocera and the Phyllopods, which by 

 the females are partly deposited on plants, and partly simply ejected 

 into the water, have to stay there a considerable time, sometimes even 

 several months, till they develop, but are in many cases, e. g., by the 

 evaporation of the water in shallow ponds or ditches, laid entirely dry 

 for a longer or shorter period. For most of the varieties of the Phyl- 

 lopod the consequent imbedding of the eggs in the hardened mud seems 

 to be an essential condition for their development." 



Professor Benecke told me that the freezing of the eggs also seems 

 to favor their development. Dubisch has observed for a number of 

 years that in ponds which have been absolutely laid dry for a consid- 

 erable period, a very large number of diminutive aquatic animals will 

 develop immediately after the ponds have been filled with water. He is 

 of opinion that it is an advantage to have the ponds filled with water 

 for as short a period as possible prior to stocking them with young fry 

 of the carp, in order that these small animals which are to serve as 



