386 



deep the greatest mortality was among the darters and the minnows 

 (Notropis and Pimephales) . These died in numbers in the aquaria, 

 no darters at all being kept alive. After a number of trials a series of 

 experiments was performed to demonstrate the cause of the death of 

 the fishes (darters, BtJieostoma cocridcuin, and minnows, Pimephales 

 notatiis). The procedure was as follows: 



Twenty-two 5 in. x 8 in. battery jars were set in a water bath, — the 

 tank into which and out of which tap water flowed, — ready for filling 

 with water modified variously, by boiling, aeration, and the addition 

 of various substances as shown in Table I. Minnows and darters were 

 given separate jars. 



The following table shows the results. 



Table I 



Average Life up to Ten Days. 



Tivo individuals in each condition except ichere otherwise stated. 



These experiments should be repeated but were sufficient to indi- 

 cate the proper precaution as to quantity of water and rate of flow. 

 As they stand they indicate that the addition of sulphuric acid in the 

 quantity given does not improve living conditions in the boiled water 

 for either darters or minnows. In the case of the aerated water the 

 results are contradictory. Iron sediment does not seem to be a factor 

 causing death. The number of fish to a given amount of water ap- 

 pears very important, and indicates that the losses were in part due 

 to an insufficient flow through the aquaria. The fishes evidently add 

 some waste products to the water which are of a non-gaseous charac- 

 ter and thus are not removed. It appears that there should be about 

 one liter of zvater for eacJi gram of fish in the case of the two species 

 studied. Less is doubtless sufficient for many species though it was 

 thought best to use 4 liters of HoO in which to kill a 4-6 gram sun- 

 fish in a bottle. 



