106 PHTSOSTOMI. 



with the hand. After a short period the eggs become adherent but gradually absorb 

 water, distend and are like little round balls. The period for which milt will remain 

 serviceable after removal from the fish is an interesting subject. On October 23rd, 

 1874, some was obtained at Howietown at 9 a.m. from a Salmo fario, then carried 

 to Loch Leven in a tightly corked tube, and used at 1.20 p.m., the impregnation 

 being perfect. Ova or milt may be kept alive for some hours, but on the addition 

 of water, death rapidly occurs. 



Respecting the artificial propagation of these fish, I think I can do no better 

 than give a summary of the excellent article on " stocking," by Sir J. Gibson- 

 Maitlancl. Skill and knowledge are requisite in order to select the fish from 

 which the milt and the ova are to be collected, and likewise to ensure perfect 

 impregnation. The ova should be laid down on glass grilles in the hatching 

 boxes from whence dead ones can be readily removed before the fungus which 

 grows upon them has time to damage by spreading to such as are in its vicinity. 

 When the eyes of the embryo commence to be visible an increased supply of 

 oxygen is necessary. When the embryo is sufficiently developed to enable the 

 eggs to be handled with impunity, they may be packed in trays, on damp swans- 

 down, and forwarded to their ultimate destination. Care has to be taken that the 

 water for the hatching-house is constant in its supply, equable as to its tempera- 

 ture, and not loaded with sand or any impurities, that frost is kept out, and 

 though early eggs are the best, eyed ova should not be sent to a cold locality where 

 it would have to battle with one or two months' continuous frost, on the other 

 hand transmitting it to a warmer climate care must be taken to meet the tempera- 

 ture en route which almost of necessity sets the eggs hatching. 



These eyed eggs are turned down into artificially and carefully constructed 

 redds, scattered all over the district in close proximity to the best feeding grounds 

 and ripples for the fry. Such absolute purity of the water flowing over the redds 

 is not required for eyed ova as it is for the eggs prior to this period, still 

 discoloured water should never be employed. It is also requisite that the redd 

 be situated near a stream of less pure water, as the absence of fine particles so 

 necessary for the health of the embryo, is not satisfying to an active young trout 

 of a few weeks old. A natural river temperature of 50 will always produce 

 ample food for the young fry. Prior to the absorption of the umbilical sac they 

 should not be placed in ponds or muddy water. They will not bear much 

 handling but bear carriage very well : a 40-gallon tank being sufficient for the 

 conveyance of about 15,000 which have been feeding for more than a month, 

 except for very long journeys when a supplementary small tank requires to be 

 added, which altogether saves the necessity of handling the fry. They can be 

 reared in small properly constructed ponds and subsequently turned into deep water. 



The normal period eggs take hatching is found when the water is kept at about 

 4410 degrees to be as follows at Howietown : Salmo fario, 71 days ; S. levenensis, 

 72 ; S. fontinalis, 73 ; 8. levenensis crossed by S. salar, 75 ; and 8. salar, 77 days. 

 But as already observed lowering temperature delays hatching, increasing it 

 hastens such on (see pages 65 and 107). 



For the purpose of stocking pieces of water with trout, either eggs or young 

 fish may be obtained from a breeding establishment. It is highly desirable, prior 

 to receiving such, that a careful examination should be made that the nurseries 

 do not contain their enemies, as bull heads, Cottus gobio, which will eat them as 

 rapidly as it can find them. At the Howietown fishery* it is suggested that 

 streams with sediment in the water or a liability to floods are unsuited for 

 depositing ova, and fry are recommended instead. 



In transmitting ova those which are partially eyed are recommended, and are 

 laid down in gravel redds in some small streams contiguous to the rivers or lakes 

 it is desired to stock. Eggs being kept in glass grilles give the strongest embryos 

 and healthiest fry. 



The time necessary for preparing young trout for transport varies from three or 

 four days in the case of yearlings, to as many weeks for large examples. The 



* Circular, dated Howietown, Stirling, 1882. 



