THE HISTORY OF FISH-CULTURE. . 507 



ments, at the comparatively high temperature of 43° Fahr., the young 

 fish desrelop aud require animal food as early as February, a season 

 of the year at which it is impossible to get iusect-larvce ; it is there- 

 fore necessary to feed the fish on chopped meat, which, besides being 

 expensive, changes the nature of the water and occasions a loss of fish. 

 In our establishment, however, the development progresses more slowly, 

 so that the young fish, which at first requires no food (the umbilical 

 bag, as we have said before, is during this first stage of development 

 absorbed by it,) is hatched in April, and becomes a young fish in the 

 middle of May, when a large variety and abundance of suitable food can 

 be found in every sheet of water. This food consists of living aquatic 

 animals and insect-larva?, which are gathered with muslin nets. At 

 the end of May the young of the ablet, {Cyprinus alburnusj L.,) taken 

 immediately after being hatched, are added to this food. 



During the period of raising the young fish in the establishment, 

 special care must be taken to i)revent the drowsiness or sleep of the young 

 fish. In a low temperature everything works well, but as soon as the 

 temperature of the water is elevated, the young fish show a certain 

 restlessness in their movements ; they gradually seek that part of the 

 apparatus which- receives the water fresh from the feed-pipe, and there 

 they gather in compact masses ; their respiration is accelerated, the 

 mouth remains open, and the gills move with an effort ; then the tail 

 and head grow pale, and finally the fish dies. This sickness increases 

 in proportion to the heat of the water; and the more sudden the tran- 

 sition from cold to hot the quicker does the young fish die. This circum- 

 stance is explained in the following manner : Water, like all liquids, has 

 the property of absorbing gases. The quantity thus absorbed increases 

 when the temperature gets lower, and is less when the water is hotter. 

 This property of water is especially important with regard to oxygen, 

 which is one of the elements of the air, and which can continually dis- 

 solve in water. The absorption of oxygen by water has an immense 

 influence on the life of fish. The young fish through its gills is con- 

 stantly inhaling oxygen contained in the water, which passes into its 

 mouth and decomposes its blood. At the same time it ejects with the 

 water carbonic acid, which is a superabundant element in its organiza- 

 tion. If the water contains less oxygen than is required to oxidize the 

 blood, the gills change their lamellae, and their fringes agglutinate, de- 

 compose, are covered with parasites, and the want of oxygen necessa- 

 rily brings about the death of the fish. The necessity of oxygen forces 

 the young fish toward the place where the water has not yet become 

 saturated with carbonic acid, viz, toward the opening through which 

 the compartment is fed with water. Each fish seeks to drive away the 

 other to get sooner to the fresh water ; the feebler ones have to give 

 way, become still feebler, and perish on account of insufficient respi- 

 ration. To avoid this suffocation of the young fish, the following methods 

 are employed at Mkolsky : 



