212 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the age and condition of the eggs, but also with the condition of the water. If the water 
is muddy, the motion should be quite rapid, rapid enough, in fact, to prevent mud 
settling either on the eggs or in the bottom of the jar. Under ordinary conditions of ^ 
clearness (and absence of glutinous coating) the best motion will be found to be that 
which readily brings the dead eggs to the surface. After the hatching has progressed 
far enough to dispose of a portion of the eggs, there is, of course, less resistance to the 
current and it should be reduced by shutting off a part of the supply or by slightly i 
lifting the central tube. In fact the motion should be reduced somewhat when i 
the hatching-out begins. If the motion is not reduced from time to time as the i 
hatching-out progresses it will be found that the shells will be carried over into the 
receiving tank with the fish, and being very light, will be drawn against the outlet- 
screen, soon causing an overflow. The motion should be so gentle at the time of the 
greatest hatching as barely to induce the fish to swim out of the jar and leave their 
cast-off’ shells behind. Under the combined conditions of very healthy eggs, bathed in 
bright direct sunshine, the hatching is so rapid that the combined effort of the swarm- , 
ing mass of young fish will establish sufficient current to draw some shells over into the ' 
receiving tank. This can not be entirely prevented, but may be modified by placing a 
screen between the jar and the light. The shells under normal conditions remain and ! 
form a cloud-like layer above the mass of working eggs. As they accumulate in quan- 
tities they should be removed by shoving down the outlet-tube until they are drawn up 
with the escaping water. A good plan is to draw several jars 
in succession, catching the “draw-off” in a large pan, from 
whence any fish coming over with the shells may be ladled into 
the receiving tank. Towards the latter part of the incubation 
it will be noticed that a remnant of eggs will be very long in 
hatching. These eggs should be poured into a large pan and 
exposed to bright sunlight. The pan should be clean and 
bright. It is-not recommended to put over 5,000 eggs in one 
3-gallon pan. After a lapse of five or ten minutes, depending 
upon the stage of the eggs and intensity of the sunlight, the 
eggs will all be hatched out and the fish may be ladled into the 
receiving tank. 
Sometimes in the course of hatching it may be found 
necessary or convenient to break the connection between the 
rubber tube and the jet cock. The handle of the jet cock may 
wear loose, so that the current of water drags in bubbles of 
air, mud, trash, iron rust; or small fish will occasionally clog 
the jet cock, stopping off the supply; or it may be desired to 
move the jar to another part of the hatchery. Any of these 
conditions would necessitate breaking the connection between 
the feed-tube and the jet cock, filling the former with air. 
When the connection is broken, be careful that the rubber 
tubing attached to the glass feed-tube does not drop down and 
siphon the eggs from the jar. In reconnecting it will be neces- 
sary to again expel the air from the feed-tube before turning on 
the water. To do this without unscrewing the jar top, draw 
the feed and outlet tubes up high in the jar until the ends are 
Fig. 3. 
