38 SALMONID^ OF BRITAIN. 



the air-holes were plugged with ice, for a very severe frost had existed for several 

 days. Agitation of the can had prevented the surface of the contained water 

 freezing, but on emptying out the eggs which were free, it was found that the entire 

 inner surface of the can was a solid" incrustation of ice, wherein about one-fourth 

 of the consignment of eggs were imbedded. The next morning there was no 

 change, although the temperature of the contained water had risen from 

 31° to 33° Fah. ; still it was not until 6.30 p.m. that the ice in which the eggs 

 were imbedded could be extracted, or about 54| hours after the can had left 

 Stirling. Here was a case in which eggs were frozen in such a manner as 

 might be expected to occasionally take place when in their natural redds, but 

 although some survived longer than others, the contained embyros were insuffi- 

 ciently developed, and none lived to be hatched. On January 19th, 1886, thirteen 

 ova were taken from a hatching-tray wherein the unfrozen eggs were, and these 

 were placed in water in an unglazed flower-pot saucer, and left out-of-doors to 

 freeze. The next morning the surface of the water was frozen, and by the evening, 

 at 8 P.M., it was a solid block of ice, in which the eggs were imbedded. On the 26th 

 a thaw set in, and by mid-day all the eggs were thawed out ; one was found dead, 

 and the rest were placed in a^ tray in the hatching-house. On February 24th, two 

 died, nine during the first seven days in March, and the last within forty-seven 

 days after their having been frozen. It would thus seem that freezing is fatal to 

 these eggs, either immediately or after a varying period, and that ova once 

 embedded in a block of ice cannot be expected to survive. Consequently a very 

 severe frost may prove to be most destructive to salmonoid eggs, should the water 

 in the redds be frozen.* 



The depth of water at which these eggs may be incubated is also important, 

 for when redds are disturbed the contained ova must be washed away down stream, 

 and should they not be consumed by their enemies, more especially voracious 

 fishes, it has been surmised they perish, due to the depth into which they have 

 been carried. In some experiments which were triedf it appeared that trout eggs 

 may be incubated in still water, changed daily, at least as deep as 26 inches, the 

 greatest depth at which such was attempted. 



Deposits of various kinds, some noxious, others merely acting mechanically on 

 the egg by smothering it, and thus causing its death by the process of preventing 

 the due aeration of the contained embyro, may be occasioned in various ways. 

 These sediments, if excessive, may be immediately fatal to the embyro or to the 

 young fish, causing their destruction by suffocation, or such may be deferred 

 owing to its being incomplete. Consequent upon certain legal questions involving 

 the inquiry whether peaty water could do injury to trout eggs, a series of 

 experiments were undertaken at Cheltenham, and from which it appeared that 

 only about 50 per cent, of the eggs were fertile in peaty water, while 96 per cent, 

 hatched in water wherein there was no peaty solution : also that spates of peaty 

 water are more fatal to these eggs than their being continuously in a peaty 

 solution : while the effect of the sediment is to arrest development, especially in 

 the head, and inci"ease the size of the eye. J 



* December 28th, 1885, twenty trout eggs were taken from a hatching- tray and placed in an 

 artificial redd constructed of fine pebbles, which had been previously boiled for some time ; and 

 for periods from four to six hours daily, until February 25th, this redd was kept uncovered by 

 water. On March 27th the two first eggs hatched on the same date as those in the trays wherein 

 a constant supply of water had been kept maintained. 



t On December 24th, 1885, a paraffin cask, which had been well charred inside, and subse- 

 quently kept filled with water for a month, was placed in the hatching-house at Cheltenham. 

 For the purpose of the following experiment a blacksmith made an iron rod 34i inches long, and 

 half an inch in diameter, with cross bars every six inches projecting three inches on either side. 

 Three small trays of perforated zinc were securely fixed to these cross bars, the upper being two 

 inches below the surface of the water, the next fourteen inches, and the lowest 2G inches. The 

 water in the cask was changed daily until February 22nd, or for about seventy days, when the 

 zinc trays were transferred to a hatching-tray. In the eggs from the upper tray the first hatched 

 IVIarch 24th, two on the 25th, and two on the 26th, while two died. Of those from the middle 

 tray the first hatched March 23rd, the second on the 24th, the two others died. Of those on the 

 lowest tray, or 26 inches below the surface, one hatched March 25th, three on the 25th, one on 

 26th, and one died. 



J Having obtained some moist turf or peat cut from the vicinity of Earls Burn, near Howietoun, 



