186 



BULLETIN OF THE UNITED STATES FISH COMMISSION. 



EXPERIMENTS. 



A saturated salt solution kills the protozoa instantly, while the young trout, upon 

 being transferred to it from fresh water, are killed in 10 to 40 seconds. 



By placing salt at the bottom of a deep (about 4 feet) aquarium and allowing a 

 constant supply of fresh water to run in with as little commotion as possible, we obtain 

 a strong salt solution at the bottom, with a layer of fresh water at the top, while the 

 water at different depths will be of different degrees of salinity. As the salt gradually 

 dissolves, the fish seek the upper half of the aquarium as their abode, but frequently 

 dive down into the briny water, sometimes even wallowing in the salt for an instant. 

 The fish will live almost indefinitely in an aquarium arranged as just described, as has 

 been demonstrated at the aquarium at the World's Fair, and elsewhere. As the para- 

 sites leave the fish they will, however, be killed upon reaching the salty water. 



1. Saturated salt solution. 22° C. 



2. Saturated salt solution. 22° C. 



3. Saturated salt solution, 50 ce. ; lake water, 



500 cc. 22 u C. 



4. Saturated salt solution, 50 cc. ; lake water, 



1,000 cc. 22° C. 



saturated salt 



5. 9:45 a. m. Lake water, 500 cc; 

 solution, 1 cc. 22.8° C. 

 9:46 a.m. Saturated salt solution added, 

 9:47 a.m. Saturated salt solution added, 

 Saturated salt solution added, 

 Saturated salt solution added, 

 Saturated salt solution added, 

 10:02 a.m. Saturated salt solution added, 

 10:03 a.m. Saturated salt solution added, 

 10:05 a.m. Saturated salt solution added, 

 10:06 a. m. Saturated salt solution added, 



9:48 a.m. 

 9:53 a.m. 

 9:59 a.m. 



Total saturated salt solution, 50 cc. 



6. Lake water, 1,000 cc. ; saturated salt solution, 

 150 cc. 24° C. 



Lake water, 3,000 cc. ; layer of ordinary salt 

 on bottom of jar. 23.5° C. 



Young trout (4 months old) overcome in 30 sec- 

 onds ; removed to fresh water, but did not 

 recover. Parasites on fish for the most part 

 alive. Those which fell from the trout during 

 its rapid movements and struggles were killed 

 instantly. 



Young trout (4 months old) affected instantly; 

 killed in 10 seconds. Parasites on fish still 

 alive. 



Young trout affected immediately ; overcome in 10 

 seconds, but revived in fresh water. Parasites 

 on fish still alive. 



Two young trout att'ected immediately ; overcome 

 in 10 seconds; revived in fresh water; placed 

 again in solution No. 4; remained unaffected 

 for 12 minutes, when they began to weaken; 

 transferred to fresh water they revived again. 

 Parasites on fish still alive ; protozoa in water 

 dead. 



9:45. Young trout placed in solution No. 5. 



Trout begins to weaken at 10 :18, is gradually over- 

 come, but revives in fresh water. Returned 

 to same solution it is overcome in 40 seconds, 

 but revives again in fresh water. Parasites 

 on the fish are all alive, but those which have 

 dropped into the water die instantly. 



(a) One trout overcome in 4 minutes. 



(b) One trout overcome in 5 minutes. 



(c) One trout overcome in 12 minutes. 

 Parasites on fish alive. 



(c) One trout overcome in 15 seconds. 



(b) Five trout remain alive 4 hours and are then 

 taken out. 



1 hiring experiment the fish frequently showed 

 signs of weakening and were then removed 

 temporarily to fresh water and returned to the 

 solution immediately upon recovery. Para- 

 sites on fish still alive; those which fell into 

 the water were killed. 



Iii the above experiments, except Nos. 1 and 2, fresh air was continually forced 

 through the water. 



