How to obtain it. 195 
ment of the fish from this point is a most interesting study, and well 
worth the attention of anyone who is interested in such matters. 
The hatching boxes should be kept as clean as possible 
during this period, for although the alevins themselves will scour 
the floor and keep clean the space immediately around them, yet 
they are liable to be very seriously incommoded by dirt in the 
water. Anything ofa fibrous nature is apt to be drawn to the 
fins, in a way which must be exceedingly uncomfortable to the 
fish, even should it not in the end prove fatal. 
During the ‘‘alevin” stage of the trout’s existence there 
should be very little trouble as a rule in the hatchery. The daily 
watchfulness as to the water supply, cleaning of filters, and picking 
out any dead alevins that may occur, forms the chief work, so far 
as the young fish are concerned. A sharp look-out should be 
kept for intruders in the boxes, for it is quite possible that some 
creature may find an entrance in some unlooked-for way or other. 
Rats I have already mentioned, and mice are in a degree almost as 
bad, and they are much more difficult to keep out than rats, as 
they can get through such a much smaller hole. 
In the early days, when my hatcheries were not vermin-proof, 
a very sharp look-out had to be kept, and recourse had to constant 
trapping, but, notwithstanding, it was found absolutely needful to 
make the buildings thoroughly proof against these enemies. 
After this had been done, as I thought, still they came, and it 
was a puzzle to find out how they entered. At last it was found 
that they came through what seemed an impossible means of 
entrance, immediately over one of the doors. This was stopped 
with broken glass and cement, and for a few days all was clear. 
Then they came through the roof, but this means of ingress was 
also stopped, and now the only chance to get in is by the door, 
when it is open. I say, when it is open, because it is carefully 
kept closed, except at times when anyone is passing in and out. 
There is an excellent trap which I now use, and which I will 
guarantee will keep any place clear of rats if properly worked. 
I will describe it later on. 
There is a possibility in some hatcheries of the larve of 
water-insects getting into the boxes, and they are destructive. 
Their presence is easily discovered, though. Some morning, in 
