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CONTRIBUTIONS TO THE BIOLOGY 

 OF FRESHWATER FISHES 



By W. RUSHTON, A.R.C.S., D.I.C., F.L.S. 



I. THE EFFECTS OF VARIOUS IMPURITIES IN A STREAM ON 

 THE LIFE OF SPERMATOZOA OF TROUT AND YOUNG TROUT 



At the suggestion of the owner of a salmon and trout stream in Banff- 

 shire, which of late years has become very polluted owing to various 

 trade products, a series of experiments was undertaken to find out 

 whether the various trade wastes have any effect on the fertihsing power 

 of the spermatozoa. 



The method adopted was to have crude samples of every type of 

 trade effluent collected when at its worst and delivered in London. On 

 receipt of it the milt and ova were extracted from fully mature fish, and 

 submitted to the various effluents in order to test the power of fertihsa- 

 tion in the presence of the impurity. When the milt and ova had been 

 in contact a certain length of time the ova were placed in an artificial 

 redd in running water and the number of eggs which hatched out and 

 gave rise to normal embryos noted. 



The whole of the work had to be done between December and March 

 of the following year, as it is only in the late fall that fertile fish are 

 obtainable. The trade effluents of the particular stream under con- 

 sideration are waste products from six distilleries, consisting of spent 

 malt products and yeast cells from the first distillations. Effluent from 

 a tweed mill where wool-scouring, dyeing and weaving are carried on, 

 and crude sewage from the town. 



The effluent samples were collected as far as possible just as they were 

 entering the stream except in the case of the cloth mills where this was 

 impossible, owing to the mill standing over the stream, and only a 

 diluted sample was obtainable. 



The method of obtaining the ripe ova was to take mature brown 

 trout and, after drying the fish as far as possible, by gentle pressure to 

 extract the eggs into a clean dish ; the same procedure was adopted in 

 regard to the milt, great care being taken to prevent water mixing with 



