and SchSperclaus (1931). In neither instance, 

 however, was the material from experimental 

 infections, i.e., the fish were not exposed to 

 infection under controlled conditions. SchHper- 

 claus (1931) held newly feeding fry in infested 

 ponds for 11 days and then observed them in 

 aquaria supplied with uninfested water. Symp- 

 toms of black-tail disease (tail -chasing whirl 

 and black tail) developed at 35-46 days. The 

 fish recovered in about 2 months but the infec- 

 tions were not verified histologically (SchSper- 

 claus, 1961, pers. comm.). It is not known 

 for certain exactly how they acquired the para- 

 sites . 



The sporoplasm becomes the multinucleate 

 amoeboid trophozoite that can be seen in the his- 

 tological sections of cartilage from about 40 days 

 post infection (SchSperclaus, 1954) to 3-4 months. 

 The trophozoite grows and the nuclei divide and 

 differentiate to produce units known as pansporo- 

 blasts, containing 12 nuclei each which event- 

 ually produces 2 spores at about 4-6 months . 

 Spores are probably released after the death 

 and disintegration of the fish . However, 

 Uspenskaya (1957) has found spores in various 

 organs other than skeleton and believes that 

 some make their way to the outside through the 

 intestine during the 4-9 month phase of the 

 disease. Spores have been found in fish up to 

 3 years of age (Uspenskaya, 1957). It is assumed 

 that newly feeding trout fry become infected by 

 ingesting spores which have been released from 

 the skeleton and associated lesions of older fish 

 that have died or been crushed. However, no 

 one has reported on establishing the disease 

 experimentally by feeding fresh spores to fry 

 or by holding the fry in water to which fresh 

 spores have been added. 



In an attempt to reproduce the life cycle 

 and to test disinfectants, we set up 47 experi- 

 ments in 1959. Spores were fed to 47 lots of 

 6-24 rainbow and brook trout each. The fish 

 ranged from 2 weeks to 4 months of age. In- 

 dividual lots of the spores were treated with 

 one of the following: sodium hypochlorite, 

 sodium hydroxide, formalin, phenol, calcium 

 oxide, zephiran chloride (Roccal*^), calcium 

 cyanamide, drying, heating, freezing, and others 

 (94 fish) served as controls. The aquarium 

 water was not changed until absolutely necessary 



in order to retain the spores. Compressed air 

 was supplied and the aquaria cooled by immer- 

 sion in running 54° F . spring water . Of the 

 entire group of fish, 17, including two controls 

 in uncontaminated, but otherwise similar aquaria,, 

 developed whirling symptoms at 12 to 19 days 

 post exposure. Only one developed black tail. 

 Whirling (tail chasing type) alone cannot be used 

 as proof of JM. cerebralis infection because we 

 have seen whirling at two hatcheries where no 

 spores could be found. Presumably other con- 

 ditions, perhaps certain types of malnutrition, 

 can cause whirling. Therefore, we attempted 

 to verify our studies by identifying the develop- 

 ing stages of the parasite in histological section^ 

 but we were not able to demonstrate any para- 

 sites. 



In 1960 seven lots of 10-75 (total 290) 

 newly feeding rainbow fry were placed in 

 aquaria at 54° F. Suspensions containing many 

 spores were prepared by homogenizing infected 

 yearling trout heads with the Waring blendor or 

 macerating with mortar and pestle. This mat- 

 erial was added to the aquaria just after the fish 

 had begun to feed and the water was not changed 

 in order to retain the spores. Another lot was 

 also fed such a suspension for 6 days. All fish 

 were kept in the "contaminated" water for 5 to 

 14 days and then transferred to running spring 

 water. Whirling was seen in a very few at about 

 2 weeKs but no infections have been verified and 

 no symptoms persisted. From these experiments 

 we assume that a transport host, pond envoron- 

 ment, or different water condition is necessary 

 for transmission of the disease. Another possi- 

 bility for our negative results is that we may 

 have rendered the spores non-viable during 

 handling. We were not able, however, to as- 

 certain any damaging factors and the spores 

 appeared normal microscopically. 



We have likewise been unable to infect 

 very young bluegills with the spores of a dif- 

 ferent Myxosoma sp. that occurs in bluegill 

 cartilage . 



In an attempt to determine whether fry 

 can become infected prior to feeding, 4 lbs. of 

 rainbow sac -fry were kept at the affected Benner 

 Spring Hatchery for 10 days and then brought to 

 Leetown, before feeding, for rearing in uncon- 



