SALMON AND TROUT CULTURE. 445 
hatching apparatus itself. Storage tanks or reservoirs will still be 
necessary in most cases, as the water should not be taken from 
a very great pressure. Fish are as frequently killed by water 
that is too highly charged with air as from a scarcity of water. 
It is perfectly possible to hatch a limited number of eggs 
in a few oyster shells, a soup plate, or a frying-pan—I was 
almost saying an old hat—by which I would convey that the 
material of which hatching troughs are constructed is not of so 
much importance as the ¢veatment of the ova placed in them. 
The most important thing ‘is the water-supply ; if this deposits 
much sediment, filters must be used. 
There are different opinions as to the structure of hatching 
troughs, Whilst some prefer the ‘glass grille’ system, ‘others 
find slate or metal troughs, wire gauze, or perforated zinc trays 
answer equally well. The glass grille system appears to me 
extravagant only as far as space is concerned. Lord Lauder- 
dale says that in his water this system produces stronger fish. 
The first cost of the glass is certainly greater, but it entails no 
annual expense, and has the advantage of being an almost perfect 
non-conductor of heat or electricity, the latter being an impor- 
tant factor in hatching, and as yet insufficiently studied. With 
the water I employ, perfectly healthy young fish are produced 
by the other methods. 
The ‘slate trough’ plan also loses much space, as it is not 
advisable to place the ova in more than one /ayer during the 
period of incubation. 
The perforated tray system, with the ‘underflow’ supply, 
will bring on very many more eggs in the same area. To 
make a comparison—upon a superficial area of one inch, twenty 
to twenty-five ordinary sized trout ova will lie; therefore to 
hatch,-say ten millions of eggs on grilles, or on the bottom of 
troughs, an area of over 300 square yards is required (in reality 
500 square yards would be necessary). In the perforated tray 
system, eggs may safely be placed ten or fifteen deep; the 
space required to bring on ten millions of ova by this method 
would thus be but a tenth or a fifteenth part; but as there is 
