Ward. — Fish Parasites and Parasitic Diseases 219 



From these tables it appears that on the whole the mi- 

 grating fishes are more heavily infected than those which arc 

 confined to fresh water during their entire existence. This 

 is conspicuously true of the Alaska salmon. In addition to 

 the migratory* fish one will pick out from the tables many 

 rapacious species as almost or fully equally infected. Such 

 are the lake trout, whitetish, black bass, rock bass, pike, 

 gar, dogfish (Amia), bullhead and some other catfishes, 

 wall-eye, and perch, in which practically every individual 

 was infected. That the degree of infection is clearly re- 

 lated to food and habits of life is evident from an examina- 

 tion of the table ( p. 226 and 227 ) in which the fish are 

 grouped by families. In the families of the catfishes 

 i Siluridse), gars (Lepisosteidse), salmon (Salmonidse), and 

 pikes (Luciidse), infection is almost universally recorded. 

 Among the sunfishes ( Centrarcfmke ) the only exception is 

 the smallest, the common sunfish ; among the perches 

 (Percidae), the small darters again are the exceptions. On 

 the other hand the stickleback, miller's thumb and moon- 

 eye are infected in only about half the total cases, while 

 among the cyprinid fishes infection is distinctly unusual. A 

 few types are represented by so few specimens that no con- 

 clusions can be legitimately drawn concerning conditions in 

 the family of the species. 



Regarding different types of internal parasites the tables 

 disclose some interesting and important conditions. Few 

 fishes shelter equal numbers of all kinds of parasites and no 

 species is recorded as heavily infected with all four groups 

 of intestinal worms. Only one,* the trout of the Great 

 Lakes, is credited with an abundance of three kinds — tape- 

 worms, roundworms and spiny-headed worms; and, 

 strangely, this is almost the only fish listed, and it is the 



*The Pacific salmon are all of them well infected by flukes and tape- 

 worms, while some of them, the king coho and red salmon, harbor a 

 generous supply of roundworms also. But, as already remarked, these 

 have brought their parasitic guests with them from the ocean and can 

 hardly be compared justly with fish limited in range to fresh water 

 exclusively. 



