Studies on a Marine Parasitic Ciliate 377 



the free living phase. Growth experiments indicate tliat the effi- 

 cient rephcation requires the carnivorous mode of feeding. The 

 strains are better adapted to the lower salinities found in mam- 

 malian tissue culture medium and in the fish body fluids. Table 

 6 gives a comparison of the osmolarities of several environments 

 the parasites are exposed to in our experiments. 



As is known from tissue culture research, a slight hypotonic- 

 ity guarantees best growth results. This rule is also valid for 

 fish tissue culture ( 1 ) although L. Griitzer obtained good results 

 with isotonic medium (6). In our case, media prepared with 

 various proportions of seawater did not give better growth than 

 media designed for mammalian cells. It has been reported that 

 fresh water ciliates lose their pulsating vacuoles and decrease 

 in body size if gradually adapted to seawater (3, 7 ) . In all media 

 used in our investigation, pulsative vacuoles were found to be 

 active. Cell sizes were larger in Melnick's seawater medium 

 than in the low salinity medium. 



A recent report (11) describes the successful isolation of a 

 genuine fish virus by means of tissue cultures of appropriate fish 

 cells. The discovered virus causes pancreatic necrosis in trout. 

 It is planned to use this virus for similar experiments as de- 

 scribed in Part 3 of this publication.* 



Tetrahymena and several other ciliates have been exposed 

 to influenza virus by Groupe and co-workers (4, 5). He empha- 

 sized the fact that the infectivity titres were reduced by a factor 

 present both in live and in killed Tetrahymena cells, while 

 hemagglutinin was destroyed only by actively growing but not by 

 starving cells. 



Our experiments indicate that poliovirus is not destroyed or 

 inactivated by feeding ciliates but a profound and apparently 

 irreversible inactivation of virus occurs in the presence of starving 

 ciliates kept in Eagle's medium. 



SUMMARY 



In our search for viruses in marine fish an accidental dis- 

 covery was made. A holotrichous hymenostome ciliate ( Tetrahy- 



* We thank Dr. Kenneth Wolf, U. S. Fish and Wildlife Service, Kearncysville, 

 West Virginia, for sending his material to us. 



