1902-3. 



Sawdust and Fish Life. 



45t 



A Stagnant Artificial Pool. 



Reference has already been made to the fact that black bass fry, 

 minnows and perch, when placed in an aquarium, invariably avoided the 

 poisonous sawdust water at the bottom. Having sunk into it once or 

 twice, it was found almost impossible to drive them into it again. Here 

 was a conflict between two fundamental instincts. On the one hand 

 was the natural instinct to hide in deep water ; on the other hand, the 

 equally natural instinct to avoid the poisonous solution at the bottom. 

 Which instinct would the fish obey if compelled to make a choice ? 



The following experiment was designed for the purpose of seeing 

 which instinct was the more powerful, and for the further purpose of 

 imitating what might possibly occur in a stagnant pool along the course 

 of a sawdust polluted stream. 



A glass aquarium 12 in. x 8 in. x 6 in. was placed in a much larger 

 vessel and a mixture of ice and salt packed in the latter so as to sur- 

 round the aquarium. The aquarium was then half-filled with white pine 

 extract which had been forming for three weeks, and which killed adult 

 fish in from one to three minutes. After the extract had been cooled 



down to 8° c, tap water at the tem- 

 perature of 13° c. was slowly admit- 

 ted to the aquarium so as not to 

 disturb the underlying poisonous 

 water. The tap water, being warmer, 

 floated clear and transparent on 

 the dark purplish extract below. 

 The clear water entered and left 

 the aquarium at the rate of 150 c.c. 

 per minute. The arrangement of apparatus is represented in Fig. 4. 



At first two minnows were placed in the aquarium. They at once 

 dove to the bottom, encountered the poisonous water, immediately came 

 up again, repeated the operation a few times, and finally remained swim- 

 ming about in the clear water. Three black bass fry, liberated one after 

 the other, went to the bottom and never came up — suffocated and 

 poisoned in the dark stagnant water at the bottom. Of two other 

 minnows dropped into the aquarium, one large one never came to the 

 surface ; the other joined its fellows in the clear water above. All three 

 soon found the end at which the fresh water was entering and remained 

 there facing the stream. 



This experiment shows what might possibly happen in pools parti- 



"'^^^ 



Fif 



