242 How to obtain it. 
many fish is considerable, and is a thing that is often not taken 
into account by practical men. It is a matter that is of vital im- 
portance, however, as the fish, although they may live, will be 
liable to be killed by circumstances which would not otherwise 
affect them. The slackening of the water supply—accidental or 
otherwise—a rush of surface water after heavy rain, or even a 
freshet, may kill a lot of them, and often the best fish are those 
that suffer under such circumstances. Do not overcrowd the fish 
therefore. 
A pond sixty feet long, four feet wide, and about three feet 
deep, will hold ten or fifteen thousand fry at first, and give them 
plenty of room to grow, but by the end of July the number should 
be reduced to five thousand, which may be left till October, 
when they should again be thinned out, or better still, put into 
larger ponds. When pressed for pond room I have put as many 
as thirty thousand fry into a nursery pond of the size just mentioned, 
but they soon required thinning out, and whilst they were in the 
pond had a good current of water running over them. It is most 
important that the water supply should be at all times ample. 
There should be more than is actually required, so that at any 
time an extra quantity can be turned on. The amount of water 
run through each set of nursery ponds should depend a good deal 
on surrounding circumstances, but from fifty to a hundred gallons 
per minute is a fair quantity, and this will keep seven ponds 
going, other things being equal. If more ponds be required, then 
an entirely additional supply of water will be needed. At the 
Solway Fishery there are several sets of nursery ponds, and the 
water from each set is conducted into a raceway, and after flowing 
with a good ripple for a quarter of a mile is again used for supply- 
ing ponds containing larger fish. 
A given supply of water will only support a limited number 
of fish, and after being passed through a series of ponds it requires 
purification. There is no better plan than allowing it to ripple 
over the stones, and to pass through a pond or even a raceway 
containing vegetation. 
In this way oxygen is absorbed from the air, and is also 
received from the plants, which, on the other hand, take up the 
deleterious matter with which the water has become more or less 
