WATER AND HATCHING TRAYS. 33 



to fresh water it becomes white and opaque, hut returns again to its clear glass- 

 like appearance if re-immersed in salt water, and this alteration on changing 

 fluids may be seen on being repeated for several successive times. 



Dead eggs are sources of great injury to the contiguous living ones, whether 

 in the natural redds or in the hatching trays of the iish-culturists, being liable to 

 byssus, a product of decaying animal substance. This, which is of a fleecy appear- 

 ance, develops long tendrils that branch out in many directions, attaching 

 themselves to all the eggs in the vicinity and mostly ensuring their destruction. 

 Its existence renders it necessary to remove* all opaque and dead ova, which 

 should be done not less frequently than three or four times a week. Another form 

 of fungus must likewise be remarked upon, this species is allied to the Hapro- 

 legnia ferax, so destructive to many of our fishes, and when it once shows itself all 

 tlie eggs will probably perish, or should any young emerge they will be sickly and 

 worthless. Difficult to perceive on account of its fineness and absence of colour, 

 it may obtain a firm hold on the eggs before the fish-culturist is aware of its 

 presence, and the cause of its existence has yet to be discovered. Dirty water 

 will not invariably bring it, nor clean water keep it away, the rapidity of its growth 

 is diminished by darkness, and increasing the flow of water and also decreasing 

 the temperature have been found in some instances to be checks, but the most 

 likely preventive is to char the inside of the trays and every piece of wood over 

 which the water which supplies the hatchery flows, or use paint or other similar 

 expedients, and keep the eggs in the dark. 



The water most suited for a hatching-housef is that from an inexhaustible 

 spring:}: of sufficient capacity throughout the year at a low temperature, as from 

 41° to 45*^ Fahr. and free from all forms of pollution ; that which rises from a 

 limestone source is preferable. When the water supplying the hatching-house, 

 as the Mill- Holme one at Howietoun, comes from an underground source it is not 

 subject to fluctuations of temperature or to floods, consequently filtering beds are 

 unnecessary, a few settling pits distributed along its course being all that is 

 required. 



The water which is intended for hatching purposes is now conducted into a 

 supply trough, and from thence distributed to the hatching-trays, and whatever 

 plan is adopted they ought to be in such a position that the attendant can obtain 

 easy access to the eggs and readily examine them in order to ascertain their 

 condition, and, when necessary, remove the dead ones. 



Hatching-trays of various forms and sizes are employed, in accordance with 

 the water supply, and either contain one layer of ova resting on the floor of the 

 tray, or placed so that a current of water§ flows under as well as over them ; or 

 there may be several trays placed one above another within a large one, while 

 from li to 1| inches of water should always be present above the eggs. The 



* One of the best plans for this purpose is the bulb syrkige, as employed at Howietoun, and 

 several other modifications are in use ; also tweezers or nippers of fine wire, a mmiature 

 spoon, or even a leech glass. 



J The hatching-house has to be modified in accordance with the locality and requirements ; 

 in cold places a more solid construction being necessary to keep out frost, or it may even be 

 necessary to place it under the lee of a bank. If it is desired of large size it should be erectetl 

 on a slope, in order to permit the hatching-trays to be placed in stair-like sequence, so that a 

 considerable fall of water may exist between the one above and that next below it. But, as has 

 been frequently observed, however adequate your house and water supply are, you are not secure 

 unless all your joints, screws, taps, &c., are kept in good working order. 



X Of course this is not always available, and water may have to be obtained from streams or other 

 sources rendering filtering necessary; but filtering, although it may clarify water, does not alwaj-s 

 remove all its injurious ingredients; while, although clear water, destitute of animal and vegetable 

 impurities, is best adapted for incubating eggs, its very absence of life renders it unsuitable for 

 young fish. River water is hable to droughts and floods, while in winter it often brings down ice, 

 IpfliVGs sticks Rud other claJjvi'^ 



§ At Howietoun, where the average temperature of the water is from 41° to 45° Fahr., the 

 supply is 10 gallons a minute to every 100,000 eggs, which flow is increased in the later stages of 

 incubation, while the hatching-trays are about 6 ft. 8 in. long and 19h inclies wide, inside measure- 

 ment; after the eggs are hatched one foot of the lower end is kept vacant, and divided oh from the 

 remainder of the tray by a screen. Where the water enters is a screen of perforated zinc, placed 

 about 8i in. from the upper end, but it slopes obliquely downwards to the floor of the tray, so 

 that no space is lost. 



