THE SPEY 153 



operating for two years. In this, in the winter of 1907-1908, a 

 series of four double tanks were placed. Three of these were for 

 testing the effluent, the fourth being a control experiment in pure 

 water. Through the kindness of the Duke of Eichmond and Gordon 

 we obtained salmon ova and salmon fry of two ages. Each pair of 

 tanks was provided with, in one case, a glass grill of ova, and in the 

 other a number of fry. One pair of tanks contained the pure 

 effluent as it came from the filter, another the effluent of 40 per 

 cent, strength, another the effluent reduced to 4 per cent. The first 

 and second were regarded as quite exceptionally severe tests; the 

 4 per cent, tanks may be regarded as probably similar to the condi- 

 tion found in a small stream below a distillery discharge after treat- 

 ment by the bacterial method. A full account of the experiment has 

 been published in the Sixth Eeport (1909) of the Eoyal Commission 

 on Sewage Disposal, in which details respecting the rate of develop- 

 ment of the ova, temperatures of the various tanks, feeding and 

 growth of the parr and smolts, etc., are given, along with a description 

 of the hatchery arrangements and full analysis of the effluent taken 

 weekly throughout the time of the experiment. The accompanying 

 photograph shows, in the foreground, the small hatchery, and just 

 behind the group of figures the bacterial filter, with above that the 

 mixing and precipitation tanks. 



It is sufficient to state here that the hatching of the ova followed 

 a perfectly natural course, the rate of hatching being in proportion 

 to the variation of temperature, and that no unusual mortality 

 occurred either amongst eggs or fry. The open nature of the 

 percolating filter resulted in a very low temperature in the effluent 

 during the winter months, and, according as the mixture of water 

 was small or great the water temperature being relatively higher 

 so the rate of development was slow or rapid. But there was 

 practically nothing to choose between any of the tanks, the ova 

 even in the undiluted effluent hatching out with as good percentage 

 as the ova in the control tank of water only. 



The young fish introduced were of two ages, eight months and 

 twenty months. These fed and throve well. Not a single death 

 occurred amongst the older fish, which were reared to the smolt 

 stage and acquired the silvery scale. A few of the younger fry 

 became pugnacious and died through fighting. A curious result was 

 that the fry in the tank containing the undiluted effluent grew more 

 rapidly than the others. This, however, was probably in no way 

 due to nourishing properties of the effluent, but to the fact that as 



