Ward. — Fish Parasites and Parasitic Diseases 211 



tory, while in this country the only references consist of 

 meager notes, scattered through a mass of other material. 

 There is no doubt that special diseases exist, but we know 

 next to nothing of their distribution or of their frequency. 

 So far as methods for the relief of the difficulty are con- 

 cerned the American fish culturists may follow with safety 

 the processes already worked out in the old world. 



Giard was the first to discuss a widespread phenomenon 

 of biological importance, which he named parasitic castra- 

 tion. This is of most frequent occurrence among inverte- 

 brates, especially Crustacea; it consists in the reduction and 

 ultimate destruction of the reproductive power in conse- 

 quence of parasitic invasion. The effect is produced directly 

 or indirectly; in the one case by the actual destruction of the 

 sexual glands and in the other by the subtraction of so much 

 nourishment that these glands remain in an undeveloped con- 

 dition and are not functional. The condition has not been 

 reported previously from fishes, but is, I think, not an un- 

 common occurrence. At least I have examined fish of sev- 

 eral species in which the sexual glands were atrophied as the 

 evident results of large parasitic infestation. One of these 

 was a rainbow trout sent me from a hatchery. This condi- 

 tion deserves careful attention, as the effect is evidently 

 serious in fish culture since it attacks the very element in 

 the fish which is of supreme importance to the fish culturist. 

 viz, the reproductive power. 



One further fact deserves especial mention. The effects 

 produced by parasites have been determined by a study of 

 the conditions in higher animals. Economic reasons have 

 limited the study almost entirely to man and the important 

 domestic animals. ' For the water-living animals one can 

 find no regular, sv>tematic, or extended studies. The casual 

 notes of investigators occupied with other problems yield all 

 the definite information at our command. Beyond this de- 

 pendence must be placed on inferences from known condi- 

 tion.-; in higher groups. It is evident without further dis- 



