Ward. — Fish Parasites and Parasitic Diseases 217 



the biology of the fish which are of the greatest commercial 

 importance and hence even in the ordinary case a mild para- 

 sitic infection is costly. When one adds the possibility that 

 at any moment a serious epidemic may break out it is ap- 

 parent how important is a knowledge of the degree oi para- 

 sitic infection, of the means by which this infection is spread, 

 and of the methods by which it may be reduced. 



So far as man is concerned almost all of these parasites 

 are harmless — i. e., they do not have the power, even if trans- 

 ported in a living condition to the human alimentary canal, 

 to establish themselves there. As the viscera are removed 

 before the fish is cooked, smoked, salted, or otherwise pre- 

 pared, such a transfer is possible only when the parasites are 

 encysted in the flesh or are found in the body cavity. In 

 the case of the eggs used in making caviar, such parasites as 

 were not destroyed by the method of preparation would be 

 carried into the human intestine and bring about an in- 

 fection. The only important parasite undoubted!)" trans- 

 ferred to man in the flesh or among the ova of the fish is the 

 larva of the fish or broad tapeworm, Dibothriocephalus lat us. 

 Infection by this species is very common in some fish-eating 

 people of Europe but, though known, is very rare in Amer- 

 ica. Cooking destroys the life of this parasite but salting 

 and smoking do not always do so. 



For some time I have been studying the parasitic worms 

 of fish and have accumulated data looking toward the solu- 

 tion of their questions. At the time of making the first col- 

 lections I published a brief note ( Ward, 1894c) on this topic. 

 Xow in the light of more abundant evidence it is possible 

 to speak with greater definiteness on the subject. 



All of the records utilized here were taken from col- 

 lections made by me or under my direction and great care 

 has been exercised to reach the maximum accuracy. They 

 relate to fresh-water fish or to such migrants as spend a 

 portion of their existence in fresh water. In all, the records 

 cover 991 fish belonging to 62 species. Only 179 fish were 

 uninfected. (Table, p. 226 and 227.) 



