BULLETIN OF THE UNITED STATES FISH COMMISSION. 439 



again derived from a fly, iufected directlj^ from a l^orth Esk salmon on 

 the 14:h of March. 



It may be safely concluded, therefore, that the salmon fui^gus is not 

 a parasite jieeidiar to that fish, but that it is a form of the ^aprolcynia 

 fera.r^ which, so far as our observations go — and it must be remembered 

 that these extend over only the quarter of the year between Christmas 

 and the spring equinox — remains devoid of oosporangia so long as it 

 infests the fish, and tends to persist in this condition for a long time, 

 even when it is cultivated on those matters upon which the SaproUgnia 

 more usually subsists. Further observation must determine whether 

 oosporangia are developed on the Sajn'olegnia, while still growing on 

 salmon, later in the year. The evidence of the fact at present extant is 

 extremely unsatisfactory ; and it is a remarkable circumstance that the 

 figures which have been published show no trace of antheridial filaments. 



That living fish may be attacked and destroyed by epidemic diseases, 

 of which a Saiyrolegnia is either the cause or the constant accompani- 

 ment, has been kno^vn for a very long time. 



Forty years ago the eminent German botanist, linger,* described a 

 disease which broke out among some carp in a pond in the Botanic 

 Gardens at Gratz, and was obviously caused by a fungus, at that time 

 known as AcliJyn proHfera, but which the description and figures given 

 by Uuger clearly prove to belong to the genus which is now distinguished 

 as Sajirolegnia, and indeed to be very similar to, if not identical with, 

 S. ferax. More or less distinctly circumscribed pale spots appeared 

 upon the skin of the back and of the fins. The fish became sluggish, 

 and sought the surface of the water. A velvety investment, formed of 

 very delicate colourless close-set threads, showed itself on the spots af- 

 fected, which rai^idly became confluent, and extended from mouth to 

 anus, and even on to the gills. The scales of the aflected parts became 

 detached, red, and swollen, and sometimes ulceration occurred. The 

 animals could no longer move without ajipearing to sufler great pain; 

 they remained at the surface of the water, lying either on their backs 

 or on their sides ; and death took place in eight-and-forty hours, linger 

 found that the disease could be transferred to perch by inoculation. 



Again, there seems no reason to doubt that the fungus which accom- 

 panied the epidemic disease affecting roach, dace, gudgeon, small pike, 

 and perch, at Ightham in Kent, of which a very full and interesting 

 account is given by Mr. Stirliug,t is to be referred to Saprolegnia ferax. 

 Here, however, ulcerative destruction of the skin does not appear to 

 have occurred, and the mortality is said to have arisen from suffocation, 

 the fungus obstructing the respiratory passages. 



Pike kept in aqnaria not nnfrequently become covered with a fungus. 



* "Sur I'Aclilya prolifera." Annales des Sciences Naturelles. . Botanique. Serie 

 III. lb-44. 



t "Additional Observations on Fungus Disease of Salmon and other Fish." Pro- 

 ceedings of the Eoyal Society of Edinburgh. X., 1879. 



