60 OBSERVATIONS ON ACCLIMATISATION OF THE TRUE SALMON. 



of this species and have so remained up to the present date, 

 though I am trusting that by perseverance with the operations 

 of artificially propagating the species conducted by me within 

 the past two years it may soon again be restored to the Der- 

 went and other southern rivers in its former abundance. The 

 questions very naturally arise as to how, when and where this 

 most malignant epidemic originated, and whether at the time 

 there were any particularly abnormal, natural or artificial con- 

 ditions associated with the infected rivers ? Further informa- 

 tion as to the precise date of its appearance, and more espe- 

 cially as to whether it occurred at or about the natural 

 spawning season of the species, March and April, or at a time 

 of drought, with the water at a high temperature, or in an 

 impure condition, would be of much service in the consider- 

 ation of these questions. The approximate date of the appear- 

 ance of this epidemic would appear to be about the year 1869 

 or 1870, periods it may be remarked, of great activity in 

 association with the distribution of the fry of the newly 

 acclimatised Salmonidse in the rivers of this colony. Is it 

 possible, it may be suggested, thatthe fungus, Saprolegnia, was 

 hitherto unknown to Tasmania and was introduced with the 

 ova of these Salmonidse, or more probably in the moss wherein 

 they were packed ? Under such conditions the germs or 

 spores, like the microbes of measles or smallpox, arriving on 

 a virgin and congenial soil, might be expected to spread with 

 devastating virulence among the aboriginal inhabitants. 

 Again, it might be asked, was the period of its appearance 

 coincident with the first introduction on an extensive scale 

 throughout the riverine districts of the colony of some 

 special fertilising manure, that might be subsequently washed 

 into the rivers by means of floods, or of the general adoption 

 of some poisonous description of sheep dip, and in either of 

 which instances the water might become so polluted as to 

 jeopardise the lives of the fish ?* In the case of sheep- 

 washing, more particularly, conducted on the large scale 

 peculiar to the Australian Colonios, associated with the 

 extensive use of caustic alkaline " dips," and at a time when 

 the rivers are usually at their lowest, it is quite possible that 

 the fish may be affected thereby in a literally wholesale 

 manner. 



The circumstance is very familiar to me of the fungus 

 disease developing itself fatally among fish in aquaria 

 supplied with water containing an excess of lime or which 

 would be popularly described as being of more than ordinary 

 hardness. When the lime is present in yet greater excess and 



* I have received authentic information of ducks being killed in a 

 rivulet in the neighbourhood of Spring Bay which had become poisoned by 

 the chemicals used at an extensive sheepwash. 



