354 



Diseases of Fishes 



growth made under favorable conditions in two days is only 

 about a third of an inch. From actual measurements of fila- 

 ments of the fungus placed in water and watched under the 

 microscope, it was found that certain threads made a growth 

 of about 3000 microns in an hour. Two others, watched for 

 twenty minutes, gave in that time a growth of 90 and 47 microns 

 respectively; and yet another filament, observed during two 

 periods of five minutes each, made a growth of 28 microns each 

 time. In ordinary cultures the rate of growth depends upon 

 the condition of the medium, host, etc." 



Professor H. A. Surface thus speaks of the attacks of Sapro- 

 legnia on the lamprey: 



"The attack that attends the end of more lampreys than 

 does any other is that of the fungus (Saprolegnia sp.). This 

 looks like a gray slime and eats into the exterior parts of the 

 animal, finally causing death. It covers the skin, the fins, the 

 eyes, the gill-pouches, and all parts, like leprosy. It starts 

 where the lamprey has been scratched or injured or where its 

 mate has held it, and develops very rapidly when the water is 



FIG. 231. Quinnat Salmon, Oncorhynchus tschawytscha (Walbaum). 

 Monterey Bay. (Photograph by C. Rutter.) 



warm. It is found late in the season on all lampreys that have 

 spawned out, and it is almost sure to prove fatal, as we have 

 repeatedly seen with attacked fishes or lampreys kept in tanks 

 or aquaria. With choice aquarium fishes a remedy, or at least 

 a palliative, is to be found in immersion in salt water for a few 

 minutes or in bathing the affected parts with listerine. Since 

 these creatures complete the spawning process before the fun- 

 goid attack proves serious to the individual, it can be seen that 

 it affects no injury to the race, as the fertilized eggs are left to 



