MacCallum. — Diseases of Fishes 155 



found in small numbers inhabiting the intestines and 

 other internal cavities without producing any obvious dis- 



I ability in the fish. In cases in which this infection was 

 more external, however, the worms by their very numbers 

 and by their blood-sucking habits had a much more seri- 

 ous effect. This was particularly striking in the case of 

 the ectoparasites of the trematode group, especially in the 

 several forms of Microcotyle, which live on the gills of 

 such families of fish as the Chaetodontidae (Butterfly 

 fishes) , and Angel fishes, 90 per cent of which in captiv- 

 ity die of Microcotyle infestation. The same may be said 

 of many of the Salmonidae which suffer from infestation 

 of Octocotylidae, etc. These worms, at any rate in those 

 fish living in confinement, increase in such numbers that 

 the gills are in many instances thickly covered with them 

 — and not only do they, with their surrounding slime, im- 

 pede the access of water to the gills but they drain away 

 the fish's blood to an extent that generally ends in a fatal 

 anaemia. Another striking example of extreme infesta- 

 tion is found in the intestine of such fish as Roccus lineat- 

 us (Striped Bass) , at times so infected with Echinorrhyn- 

 chus proteus, a nematode which embeds its hooked pro- 

 boscis in and through the gut wall in such numbers that 

 the whole mucosa is covered thickly with their hanging 

 bodies. Not only is an intense inflammation set up by 

 these embedded hooks, but the function of the mucosa is 

 precluded. Still this seems to be less fatal than the infec- 

 tion of the gills. The occurrence of larval forms of vari- 

 ous digenetic trematodes and cestodes encapsulated in 

 the muscles and other tissues of fishes are well known 

 and sometimes productive of disablement of the host, al- 

 though at times the most extreme infection may exist 

 without obviously hurting the fish. 



Of the diseases caused by the unicellular sporozoa of the 

 class Myxosporidae, so well known through the work of 

 Gurley and others, relatively little has been seen in this 

 series of autopsies, and of this disease very many more 

 cases have been seen in those fish taken fresh from the 

 sea. 



