HATCHING APPARATUS. 59 



make the ripple, otherwise your fish, when hatched, will 

 not be as strong as they might have been. At the 

 lower end of the trough there should be a copper-wire 

 screen of about eighteen or twenty threads to the inch. 

 This screen should be very carefully fitted in, and 

 should be made as tight a fit as human handiwork can 

 make it, otherwise you cannot be sure that the young 

 fry, when first hatched, will not slip through. In order 

 to be perfectly sure to get this screen safe, first exam- 

 ine the place or bed that it fits into, with a strong light, 

 and take care that every bit of sand or gravel is re- 

 moved from it. Then put down the screen, having 

 previously arranged a perfectly tight fit in the side 

 cleats, and hammer it down. 



This done, sift sand along the bottom and sides of 

 the screen, bank up with gravel to the height of the 

 transverse cleats, and sift sand about the sides again. 

 You are then as safe as you can be with regard to the 

 screen, and with these precautions you will be pretty 

 sure not to lose many fish by this most common of all 

 avenues of escape, loosely fitting screens. Should 

 any aperture be caused in the future by any spring- 

 ing or shrinking of the wood, or otherwise, calk the 

 opening with flannel without delay. Below this screen 

 should be placed what is called a trap-box, to catch 

 any of the young fry that may escape through the 

 screen above. This trap-box is nothing but a com- 

 mon box with a wire screen, which will let out the 

 water, but hold the fish that come into it. I would 

 have one at the end of every hatching trough. They 

 are a very important safeguard, for they not only save 



