86 Th irtieth Annual Meeting 



fapid. Tlu' fry liatcli aljout April 1st, and brfore the end of 

 April, in epidemic years, the mortality suddenly increases, and it 

 is found that the sacs of the fry are blotched with white. These 

 blotches spread until the sac is nearly all white, especially the 

 ai)('.\. When it reaches this stage, the fish dies. Other symp- 

 toms are apparent listlessness, indifference to light and outside 

 movements, and in consequence a scattering about on the bottom 

 of the trough instead of crowding into the dark corners as is the 

 normal habit of the fish. 



This disease was first observed in 18iM), when it carried off 30 

 per cent, of our fry, inchiding Atlantic salmon, and land locked 

 salmon, but did not touch Loch Leven trout or Swiss Lake tro\it. 

 It was, however, observed that not all of the Atlantic salmon 

 were attacked (or at any rate suffered noticeably) and in the lots 

 where it did appear its destruction was quite uneven, in some 

 cases l)arely noticealile and in others wi])ing the lot com])letely 

 out. 



!t is our ])ractice at the Craig Brook Station to preserve a 

 careful record of the character of every salmon handled at spawn- 

 ing time, to keep the s])awn taken each day separate from that of 

 every other day, and to keep u}) the distinction with tlu' fish 

 hatched through the entire season, and indeed as long as the fish 

 remain with us. In some cases, as, for instance, a female salmon 

 of remarkably large or remarkal)ly small size, or an unhealthy 

 ap])earance of fish or eggs, the ])roduct of each fish is kept by 

 itself. The position of each family in the hatchery is also noted. 

 When hatching time approaches, the large lots of eggs. ( or fami- 

 lies), are divided u]) into smaller lots of one or two tlionsand 

 each, — sometimes larger — and the origin, location and history of 

 each of these minor lots is recorded. When therefore, one of our 

 fishes dies, or does anything else remarkalile, we are a1)le to fol- 

 low back its record to the day when as an egg it rattled into the 

 ])an at Dead Brook, and sometimes to the identical mother that 

 <h-n|)|)c(| the cmhryo and the identical father that gave llie initial 

 im])ulse of life. Tliese records sometimes appear, even to us who 

 kee]) them, as somewhat laborious and fussy, but in this instance 

 of the sac-epidemic of 1<S!)0, they ha\(' enabled us to di'aw some 

 very interesting conclusions as to the inlliience of heredity in this 

 disease. 



