PRACTICAL FISH-CULTURE. 569 



proper; the other, au assistant. The first frame, which, like all the others, 

 has to be agaia well cleaned, is placed in a shallow vessel or dish of tin. 

 (PI. XVIII, fig. 4.) These vessels are to be made expressly for the pur- 

 pose ; two of them being necessary for the operation. Their size is 

 somewhat larger than that of the frames, to facilitate the manipulation: 

 their height, however, must never exceed two inches. These plates 

 have to be carefully cleaned to remove all fiitty matter and oxide of tin. 

 Into one of them the eggs are emptied ; in the other the impregnation is 

 performed. 



The dish is nearly filled with river-water, like that in which the 

 hatching is to take place, of from 72° to 82° F. ; its temperature shall 

 be 18° to 220 E., (72o to 8I0.5 F.) Then the frame is placed upon 

 the water, and the eggs slowly dropped upon it. The fish is moved back 

 and forward just above the frame, so as to prevent too much crowding 

 of the eggs. As soon as the eggs adhere, the frame is reversed, and 

 the other side treated in the same way. After ten to twenty sec- 

 onds, this frame, evenly covered with eggs, is removed to the other dish, 

 containing about one inch of water; the milt is then added, or may have 

 been added while the second side was receiving the eggs. Yec there 

 must not be too long an interval between the operations, since the life 

 of the zoosperms of these Cyprinidcc is frequently of very short dura- 

 tion. In carp it is scarcely two minutes. The second frame is treated 

 in the same way, while the assistant carries the first to the hatching- 

 box, which ought to be, if possible, at the very place where it is to 

 remain. A repeated addition of fresh zoosperms to the impregnation- 

 dish is advisable. In the same manner, all three frames, with impreg- 

 nated eggs on both sides, are placed in the hatching-box. The outer 

 frame of this box must be stout enough to keep the perpendicular frames 

 well in place, so that they can neither warp nor fall down. The box must 

 be set where the stream does not exceed twelve inches in depth, with a 

 scarcely perceptible current. One inch a minute is the greatest allow- 

 able velocity, just enough to carry fresh water and air. But the appa- 

 ratus can also be used in stagnant water. The canvas cover is only laid 

 upon the box when the heat of the sun is most intense— perhaps from 

 noon to 4 p. m.— for too much suu Is just as injurious to the develop- 

 ment of the eggs as darkness. 



Every day the apparatus must be inspected and dead or sterile eggs re- 

 moved. Pincers of wire, about three inches long, and which may be made 

 by one's self, are convenient for the purpose. After three weeks, the eggs 

 will be hatched, and the young fish may be removed to ponds or lakes, 

 wherever wanted. The hatching, in the same manner, can be done in 

 ponds. 



Still another mode of breeding is in use here as well as in Xorth Ger- 

 many and on the Danube. Employing no frames, it is cheaper, yet less con- 

 venient for an observer, as the eggs mostly remain hidden and invisible. 

 It has, however, the advantage of simplicity, and thus may be applied 



