of the Fishery Hoard for Scotland. 



77 



My original intention to allow about twenty -four hours for the trans- 

 ference from pure salt to pure fresh water was departed from after 

 reflecting upon the short tidal estuary of the neighbouring river Dee 

 and the supposed rapid transference which took place under natural 

 conditions. The time was therefore cut down to approximately that of 

 a single flood-tide. From the distress shown by the fish it would seem, 

 however, that even at a river mouth where no natural estuary occurs 

 salmon, before entering fresh water, become accustomed to the influence 

 of the river as it passes out into the sea, and that they do not at once, 

 even in summer, swim straight in and immediately ascend. Conversely 

 we have already noticed that kelts descending from the small streams of 

 the West Highlands, where spawning operations are rapid, accumulate 

 and appear to lie for a short time in brackish water. 



Whether or not the unduly rapid transference into fresh water caused 

 the sea-lice to sicken also is uncertain. But even allowing that this 

 may have been so, it will, I think, be a surprise to many to know that 

 the sea-lice remained attached for six days, and that after the water had 

 become quite fresh, at a temperature of 55° F., a single parasite remained 

 on one fish for five days and on the other for four days. 



W. L. Calderwood. 



