446 SALMON AND TROUT. 
sometimes an interval of as much as three months between the 
first and last ova obtained, a second crop is laid down, and the 
boxes or troughs are used over again. 
The troughs now in general use in my hatchery are made 
of wood. They are three feet long, by one foot wide, and six 
inches deep, and supplied with water through a punctured pipe 
running all round the trough.. They are fitted with movable 
perforated zinc trays twelve inches (bare) by six inches wide and 
three inches deep. This plan, although not entirely a novelty, 
appears to have suggested itself some years ago both to myself 
and to Mr. Oldham Chambers, whose practical experience in 
fish culture generally is well known. It seems to have ori- 
ginated in my very old plan of using perforated zinc trays, into 
which were counted the ‘Fry’ previous to sending away. The 
ova it was imagined were placed in these trays, which were put 
on the bottom of the overflow trough, but of course the eggs 
perished as the water did not circulate. It was then thought 
that such trays would answer for hatching ova if raised from 
the bottom of the trough, and the water made to circulate by 
anupward current. This plan, though not claimed as an inven- 
tion, can hardly be called a modification of any other, although 
it bears some resemblance to several which have been used in 
America. It has certainly found favour among pisciculturists 
on account of its great economy in the items of prime cost and 
of space. One of these troughs costs about 55s. complete, and 
will bring on over 100,000 eggs, whilst a set of six slate troughs 
costs between 8/. and 9/, and will not contain more than half 
the number of ova. The trays may be much larger, but I 
prefer this size on account of their handiness and comparatively 
slight weight. Instead of ‘ carbonising’ the wooden troughs, I 
have them coated, as well as the zinc trays, with tar varnish. 
Silicate paint answers as well. 
Livingston Stone, in the book before referred to, says, ‘One 
form or the other of the tray system is undoubtedly destined to 
entirely supersede the old methods of hatching on glass grilles 
or on the bottom of troughs,’ 
