230 How to obtain tt. 
some four or five fish to every square inch of surface, the matter 
is widely different. If these are to be fed on natural food, it is 
clear that it must be produced for them, and that in large 
quantities. 
In order to produce crops of natural food, accessory ponds 
are required, and much may be done also by growing a large 
quantity of Extomostraca, etc., in a pond, before turning in young 
fry, so that on the absorption of the sac they may find the best 
means of subsistence close at hand. This is a subject on which 
a chapter may be written, and I hope some time to go more fully 
into it. There is a great diversity of opinion as to the best time 
for turning out trout fry. It was the custom a few years ago to 
retain them until they had got well on the feed, whereas now it is 
becoming a common practice to turn them out just before they 
begin to take food, that is just before the final absorption of the 
umbilical sac. Taking a general view of the subject, I am in 
favour of the latter plan, except in those fish-cultural establish- 
ments where everything is perfectly arranged, and the work 
thoroughly understood by skilled workers, and where the fish are 
to be reared artificially to yearling or larger size. Where fish are 
simply grown for the purpose of keeping up the supply in a lake, 
pond, or river, and are to be turned out as fry, I believe 
thoroughly in turning them out before feeding into prepared race- 
ways and ponds where that can be done ; otherwise into tributaries 
of the lake or river. Such a course saves a good deal of trouble, 
and I have seen excellent results obtained by following it. The 
little fish do best in a small tributary or raceway where there are 
plenty of water plants. A watercress bed is an excellent place. 
Should it be decided to retain the fish in the boxes, they 
must be cared for at once when they begin to look for food. 
The best thing to do is to place a tank well filled with Exéomostraca 
in such a position that the water may be run into the rearing 
boxes. Should there not be sufficient of this natural food avail- 
able, a supply of the artificial substitute must be provided. The 
simplest article to use, and one which is easily obtainable, is raw 
liver, which must be grated or chopped very fine, and the coarser 
particles taken out by screening through some very fine woven 
fabric or fine perforated zinc. I have found the latter answer 
