568 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [30] 



the carp from being frozen, special excavations are made in the bottom 

 of these ponds, where the carp crowd together in a semi-lethargic state. 

 The water of these winter ponds should be deep. But if the water 

 should freeze, it becomes necessary to make holes in the ice, so as to in- 

 troduce air into the water below. These holes are covered with sheaves 

 of reeds, having a broad base and forming a kind of roof over the holes, 

 thus preventing farther freezing. It is necessary, however, that these 

 holes be frequently examined, so as to keep them always open. 



Tillage of carp ponds. — Mr. Haack recommends the custom which has 

 been introduced, of using the carp ponds also for agricultural purposes. 

 After they have served as ponds for two or three years, they are drained, 

 and then plowed for the cultivation of grain and potatoes. According 

 to the director of the Hiiningen establishment, a pond which has under- 

 gone dry cultivation is richer in small crustaceans which form a favor- 

 ite food of fish. For instance, the eggs of the Phyllopoda will develop 

 better during a dry season. 



It will easily be understood why it is useful and profitable to use the 

 bottom of the ponds after a certain period for agricultural purposes, 

 thus utilizing the large quantity of fertilizing matter, consisting of leaves, 

 aquatic plants, animal matter, and excrements of fish, which has accum- 

 ulated in the pond ; while on the other hand it is difficult to explain 

 why ponds used in this manner should be richer in fish. Mr. Haack 

 believes that this is owing to the greater development of small crusta- 

 ceans ; but the greater abundance of these crustaceans has not been suf- 

 ficiently explained by science. We are, however, allowed to suppose 

 that the greater number of fish is caused not only by the increase of 

 small crustaceans, but also by the more luxuriant aquatic vegetation 

 which will develop in soil, which after lying dry, has been plowed and 

 cultivated, and before being again submerged has changed chemically 

 by the influence of the air and sun. Whether this explanation is correct 

 or not the fact remains and deserves to be taken into account.* 



Other hinds ofcyprinoids which arc cultivated. — As secondary objects 

 of cyprinus culture we may mention the crucian carp (Carassius vul- 

 garis), the Chinese goldfish, the Idus melanotus, and the tench. 



As regards the crucian carp (Carassius vulgaris Nilsson), I would state 

 that, compared with the common carp, it presents a great variety of 

 forms, and will interbreed with the Idus melanotus, but its flesh has not 

 hv delicate a flavor as that of the carp ; nor is its culture so profitable, 

 as ivs gr 0W th is much slower. 



The golosgh (Carassius auratus), owing to its beautiful color, is much 

 sought after at, au ornament for ponds, artificial lakes, aquariums, &c, 

 and it is therefore nil tivated to advantage. 



* Iu further proof of thh. f act Mas von dem Borne (Fischzucht, 2d eel., p. 13) re- 

 ports what took place in an oM pond near Wittingau, called the Rosenberg pond, hav- 

 ing an area of 750 acres, which CV ery three years produced only 1,000 hundredweights 

 of carp; and after having been laid di >r aud cultivated four times from 1865 to 1881, 

 produced 1,500 to 1,700 hundredweights. 



