AILMENTS AND DISEASES 



Myxosporidia. The freshwater fish-parasites of this order belong 

 to the genera Myxidium, Myxobolus, Henneguya, Nosema and Plistopora. 



Myxosporid^. These Protozoa, Figs. io2,io2a,io3, 104 and 104A, 

 are entirely parasitic and in the majority of cases live upon fishes. Dr. R. 

 R. Gurly listed 102 hosts, fishes and other aquatic fauna, inhabited by them, 

 either encysted beneath the skin, on the surface of the head and fins, or in 

 the gills, mouth, eyes, gullet, air bladder, heart, liver, spleen, stomach, in- 

 testines and almost every other part of the body. The effect of their presence 

 is a breaking up of the parts, which undergo a vitreous degeneration, the 

 growth of tumors and postules and ultimately the death of the host. 



FIG. 103. Myxobolui cyprsni, a Spora- 

 xoan parasite, encysted in the Kidneys of a 

 Carp. I . Enlarged a. Natural size of cysts. 



FIG. 104. ^yxoholus ellipsoideSj a Sporozoan 

 parasite. Greatly enlarged. 

 12 I . Cyst in the tissues of the Air-bladder of a 



Tench. 

 -i. Psorospores liberated from the cyst, highly 

 magnified. 



They are usually amoeba-like microscopic organisms, which reproduce with- 

 in or without the cyst or tissue cavity with those species which inhabit the 

 surface; and constantly within the cyst with those which inhabit the cavities 

 of the hollow organs of their hosts. Mention will only be made of those 

 Myxosporidae of the orders Phtenocystida and Microsporidiida common to 



FIG. 104A. Dermal cysts of Myxosporidium genus incert, a Sporozoan 

 parasite, on the skin of a Minnow, i. Liberated psorospores, highly magnified. 



freshwater fishes, batracians and larger crustaceans, the table showing how 

 many species have been identified and the parts they inhabit. It is seldom 

 that they have more than one particular host; that of the goldfish, for 

 instance, being Myxobolus sp. incert. Figs. 102 and io2a, and Table p. 156. 

 Myxosporidae spare no organ or elemental cell and nearly all of them 

 produce a cachexia, comparable with the cancerous tumors of warm-blooded 

 animals. They are the cause of violent epidemics among fishes and have 

 occasioned the deaths of hundreds of tons of food fishes in a very short 

 time when outbreaks of the contagious diseases caused by them have 



155 



