34 SALMONID^ OF BRITAIN. 



trajs may be made of slate, stone, pottery, or wood, being careful that, sbould tbe 

 last be selected, no odorous form is employed. Wood sbould be thoroughly 

 charred inside, or covered with tar or asphalte varnish or paint, which aids in 

 preventing the formation of fungus. Glass grilles are largely employed by those 

 who arc desirous of raising strong and healthy fry. Metal substances are liable 

 to undergo chemical changes in some waters, and should perforated zinc trays be 

 employed they should have a sufficient covering of paint or varnish.* Copper 

 should be rejected for trays. 



It has been held that deep or still waters are unsuited to the incubation of the 

 eggs of these fishes, f but, although this may be the case in natural conditions, it 

 is not found to be invariably so in artificial fish-culture. 



The eggs having been safely deposited in the hatching-trays, the fish-culturist 

 has to be careful that the supply of water is continuous and nothing occurs, so far 

 as he can obviate it, which would cause injury during the process of incubation. 

 The room should either be dark or the trays fitted with covers, as light is 

 injurious and ova subjected to it are liable to be small-eyed and weakly if hatched. 

 Of course the more pei-fect the impregnation has been the greater the proportion 

 of fertile eggs, and this saves a large amount of manual laboui- in removing the 

 useless ones. To save space, some fish-culturists have advocated several successive 

 layers of trays, a plan objected to by the majority as tending to pi'oduce weak 

 young: others again suggest that as soon as the eggs are eyed all should be washed 

 in a pan, when most of the unimpregnated ones and bad ones will turn white, and 

 then the good and clean ones might be placed in one of these trays in several 

 layers. The water should not swirl about the eggs as if they were boiling or 

 bubbling up, as such concussion would be fatal to manj', while if no appearance 

 of the embryo is observable by the fiftieth day the best plan is to throw the ova 

 away as any chance of theii- ever hatching is past. J 



I have already alluded to the forms of fungus to which eggs are liable, while 

 small eyes as seen in the embryo is a sign of weakness and observable as the 

 aesult of an excess of light or excess of cold. If it is desired to pack eggs after 



* When tish-culture was first commenceJ, it was eonsiilered necessary to follow nature and 

 deposit the eggs under gravel, which was first sifted to about the size of a large pea and then 

 boiled to destroy deleterious agencies, while such as contained much iron was rejected. Next, 

 simply charred boxes, with covers to keep out the light, were used. Cilass gi'illes or hollow rods 

 were early employed, fixed in wooden frames or resting on a strip of perforated galvanized zinc, and 

 going across the entire width of the tray, being sunk to about an inch from the bottom, where a ledge 

 of wood prevented their sinking lower and a catch precluded their rising above a desired level, as 

 from li to 2 in. below the surface. These glass rods do not quite touch one another, while a 

 passage is secured for water both above and below the eggs. Frank Buckland objected to glass 

 grilles, because " pai-ent fish do not find glass bars at the bottom of the river, but they do find 

 gravel." {Nat. Histonj of Biithli Fialies, 1880, p. 390.) While Livingston-Stone remarked that 

 simple charcoal or carbonized troughs are equally as efficacious as grilles and infinitely more 

 economical. He considered the first to be the thing for business, and the second more suitable 

 for rich men's experiments. Or the trays to receive the eggs may be made of perforated zinc and 

 the supply pipe fixed under the bottom of the box, so that the water ascends through the eggs. 

 .Similarly, these trays may be in a single, double, treble, or even in four tiers. For an account, with 

 illustrations, of a large number of processes now in use, see Day's Fiflt Ciillurc, 1883. 



f Ephemera (Hamlbook uf Anglinri, 3rd edition, 1853, p. 233) asserted that "salmon never 

 deposited their spawn in deep or still waters : if they did it would not be vivified. To Wvify 

 salmon ova impregnated by the milt, the combined influences of running water, atmospheric and 

 solar action are necessary." Sir Humphry Davy {•' Snlmonia") considered that all which is 

 required for the production of figJu's (as salmon) from the impregnated egg is a constant supply 

 of water of a certain temperature furnished with air. " The precipitation of water from the 

 atmos]ihere, its rapid motion in rivers, and its falls in cataracts, not only preserve this element 

 pure, but gives it its vitality, and renders it subservient even to the embryo Life of the fish" 

 (page 8.5). 



J Livingston-Stone very clearly explained how to recognize good from bad eggs, for although 

 it had been generally held that until the spinal column showed itself the difference between tlie 

 two was almost undiscernible, he remarked that this is not strictly true, because there is a 

 period, within forty-eight hours of the taking of the eggs, when the good can be distinguished 

 from the worthless ones. In the unimpregnated a small annular disk with a round dot in the 

 centre is seen at the top of the egg and continues until the egg turns white. In the impregnated 

 egg the disk will disappear within twenty-four hours. Eggs which after the first day show the 

 disk are unimpregnated : those without the disk are impregnated [see page 32 ante). 



