RIVER FISHERIES. 93 



the whole mixed in a common pan. The water now assumes a milky 

 tinge, from the milt of the male while the ova sink at once to the 

 bottom, and there stick fast. They appear as little round bodies 

 about three-sixteenths of an inch in diameter, (or larger, if the 

 parent be large,) of a pale yellow or an orange hue, according as the 

 parent has white or pink flesh.* They must be left in the pan as 

 long as they will stick, which will be fifteen or twenty minutes.f 

 Then the water must be gently drained off, fresh water poured in, 

 and this washing repeated once or twice. And here is the golden 

 rule for treating eggs of fishes : never touch them, but move them 

 by moving the water in which they lie. The washed eggs are now 

 ready to be spread in the hatching trough, which is done by tilting 

 the pan, and allowing them to slide gradually out, so that they do 

 not lie on top each other, and are not overcrowded. They may be 

 further arranged by agitating the water with a turkey's wing feather. 

 There may be placed about four thousand in each square, which is 

 eighteen by twelve inches. They should be allowed to remain un- 

 disturbed, but should be constantly watched, and those which die or 

 are attacked with mould, should be removed with forceps. The 

 minute vegetable growth, so fatal to eggs and even to young fish, is 

 very likely a true conferva, at least we may judge so from Vogt's 

 description of the parasitic plant that attacks the eggs of Coregonus. 

 To avoid it the precautions are : 1st, pure running water of the 

 right temperature ; 2nd, very clean gravel washed in boiling water ; 

 3rd, the use of wood for troughs which is well dried, and free from 

 knots and acid juices ; 4th, the protection from dust, dirt, and sedi- 

 ment ; 5th, protection from strong sunlight. Green discovered this 

 by observing that where a band of sunshine fell from an uncovered 

 window across the troughs the ova within that limit died. A dead 

 ovum may readily be recognized by its dull opaqueness. It looks 

 like a drop of tallow. Furthermore, the troughs should be guaran- 

 teed against mice, water-insects, and snails. Where sediment 

 chances to settle on the ova the water should bestirred with a feather 

 until the current has carried off the deposit. If spawn is to be sent 

 away, the best time is from twenty to forty days after impregnation, 

 when the eyes show through the eggs as two black specks. Take 

 live moss, with long fine stems, and wash it till perfectly free from 

 dirt, place a layer of it, whilst moist, in a tin box with holes in the 

 bottom, place therein a layer of spawn, then another layer of moss, 



* The colour of the flesh plainly does not depend on the crustacean food 

 which the trout gets, according 10 the theory of Dr. Gunther. Trout raised in 

 Green's pools, and having the same chance for food of this kind, are sometimes 

 pink and sometimes white fleshed. There is some reason to think this peculiarity 

 hereditary. 



+ This temporary sticking is an extraordinary provision of nature, to enaW? 

 the eggs to cling to the bottom, and resist the current, until the parent has.'&U.d 

 time to cover it by sweeping gravel over it with her tail. It is probable Vha,t Yo&t. 

 was mistaken in supposing the eggs of salmonida? had no viscous coa'.,; Jit is peiv 

 haps in a soluble form. (Agassiz and Vogt in Poissons d'eau douce.) v . ' ' '' ' 

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