If the water is taken from a stream, a leaf screen must be placed at some distance in front of the inlet. This may be made of a hurdle fastened to strong stakes sunk into the bed of the stream. The opening of the inlet should be at least double the size of the sectional area of the pipe through which the water is carried to the ponds, and should be some distance, a couple of feet if possible, below the surface of the water. It is a good thing to put a wire cage over the inlet, and under this a perforated zinc screen is necessary. The inlet from the stream should be so placed that it is easy to get at and clean. The best form of covering for the inlet into the pond I have seen, is a zinc cylinder, the base of which fits over the end of the inlet pipe. The part of this cylinder, which projects 18 inches beyond the pipe, is perforated, as is also the flat end. This can easily be taken off and cleaned, and breaks up the water, making it fall into the pond like a shower bath, causing considerable aeration.
The inlet from the stream should have a trap with which the water may be shut off, as also should the outlet from the pond. When the cylinder on the inlet into the pond is taken off for a minute or so to be cleaned out, both these traps must be closed. This lessens the chance of any creatures likely to do harm getting in during the cleaning. The perforated zinc screen at the inlet from the stream will probably stop any such creatures, but too great care cannot be exercised, and it is always best to be on the safe side.
Movable covers of netting over the ponds are most certainly advisable, particularly if the rearing ponds are in an unfrequented spot near a stream. On one occasion I caught four kingfishers during a period of three weeks, all of which had in some way got under some herring net, which was pegged out carefully over a rearing pond containing trout fry. I never found out how they got in, but once in they were unable to escape.
Ponds such as I have described are of course for the fry when they have reached a certain size, and have already begun to feed well. Other appliances are necessary for hatching out the ova and for the young fish when first hatched. A very good apparatus may be made from a champagne case. This should have large square holes sawn through each end, leaving enough wood to ensure strength and solidity to the box. The box should then have two coats of asphalt varnish, and the square apertures covered with fine perforated zinc. A still better box may be made at a small cost. This consists of a box with a wooden bottom and perforated zinc sides which are supported by a stout wooden frame.