246 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the flsli are allowed to pass up under the screen — tlie most important part of the 
trough — and there receive a shower bath, which keeps them clean even in muddy 
water; there is no jumping over the guard screens or the sides of the troughs, and 
there are no obstructions across the bottom of the troughs to cause the aleviiis (very 
young fry) to suftbcate, as was so often the case when the vertical screens were used. 
In feeding the fish, or examining into their condition, the screens can be either slid 
back or raised out of the way, as shown in tlie illustration. 
Hatching trays . — I prefer the hatching-trays made fully twice as long as wide, 
because they are then much easier to adjust in the troughs and hold more eggs, 
which, of course, makes fewer trays to handle and thus facilitates the work. The 
trays that I use are 13J by 28 inches (shown at C, fig. 1). T4ie sides of the frame are 
made of good pine lumber, dressed 1 inch square; the ends are dressed 4 by 1 inch, 
and are cut into the sides their thickness from the under side, forming a smooth surface 
on that side for the wire bottom. The wire used on the trays is woven with 8 threads 
to the inch, with a mesh ^ of an inch long. The wire should be well galvanized after 
it is woven, in order to prevent rusting at the laps. 
riacing the trays . — Four hatching-trays are placed in each trough and are secured 
in place by means of keys or wedges, and 
should be from 1 to 2 inches lower at the 
end toward the head of the trough, as 
shown at D, I), D, D, fig. 1. In this way 
the trays will hold from 12,000 to 15,000 
eggs with perfect safety. If we should 
be unfortunate enough to have muddy 
water during the hatching season, we use 
a tin tray with perforated bottom, shown 
at E, fig. 2. This tray is made 13f inches 
wide and 32 inches long, and sets inside 
of the hatching-trough on feet, H, raising 
it 1 inch above the bottom of the trough. 
The hatching-tray, containing the eggs 
that are hatching, is placed inside of the 
tin tray, and rests on the bracket shown at G. The little fish, as they liatch out, fall 
from the hatching-tray on the perforated bottom of the tin tray, and by their move- 
ments work the sediment through, leaving them on a clean bottom and in no danger 
of being smothered. These tin trays are also useful in counting fish, or in holding 
small lots of fish of different species in the same trough. 
N'umher of eggs to a trough . — Troughs 15 feet long will admit of 4 hatching-trays in 
a single row; each tray will safely carry 12,500 eggs, making 50,009 eggs to a trough; 
this is enough to work easily, but if it is necessary in order to make more room a 
double row of trays may be put in, one tray resting on the top of the other. In this 
way the trough Avould contain 100,000 eggs, which I consider about its full capacity. 
The troughs will carry this number up to the time of hatching, by placing the trays 
lower at one end than the other, as previously described. 
Care of the eggs . — After placing the eggs on the trays, they will need no further 
attention until the hatching begins, exce])t to keep them clean and the dead eggs 
picked off. These dead eggs may be known by their turning white. The eggs should 
be examined once every day for that purpose. After the eye-spot can be plainly seen 
