438 



Among the latter are to be distinguished the crustacean parasites of the 

 wills (fig. 10) or of the surface of the body, which may become so numerous 

 as to cause death (p. 446). Again there are various worm parasites (no species 

 of fish is exempt from its share) which, however, appear rarely to cause any 

 serious mortality. In many cases unripe stages of such worm parasites occur 

 in fish, which only reach their full development in fish-eating birds, but one 



Fig. 10.— Ergasilits with egg-sacs|from gills of sunfish. x 10. Achthercs from gills of catfish x 6. 



species of such immature forms occurring in the Pik6, and possibly also in^ 

 some Salmonoids, is the larva of Bothriocephalus latus, the broad tape-worm of 

 man. It is only found abundantly in those northern countries where fish are 

 eaten raw. Among the worm parasites may be mentioned certain thread-worms 

 which (like the guinea worm) live in the skin of their host, and may often cause 

 serious abscesses in the fins of affected fish. Certain leeches (Piscicola) also may 

 attach themselves to the skin and suck the blood of their victims with fatal 

 results. 



Obscure diseases of fish of epidemic character have not been properly 

 investigated yet. Some are no doubt attributable to bacteria, others, like the 

 salmon disease, to more visible fungus-growths such as Saprolegnia, but the 

 subject of the wholesale dying-off of fish is one which requires further looking 

 into. 



Preservation of Fish. 



Should any reader of this report desire information as to any particular 

 variety occurring in his locality, he is invited to send specimens to the author at 

 the University of Toronto. These ought to be suitably preserved before ship- 

 ment, either by putting on ice when caught and shipping promptly, or by immer^ 

 sion in a strong pickle formed of li lbs. salt, I lb. saltpetre and I lb. boracic acid 

 to the gallon of water, or in strong spirits of wine. The preservative fluid 

 used should be poured into the mouth, and if possible injected into the vent and 

 through a small slit into the body-cavity. When alcohol is used as a preservative 

 fluid it should be diluted with one-third water, so as to obviate shrinkage of the 

 tissues, and changed once or twice before shipment. The label accompanying a. 

 specimen should always give the exact place and date of capture, and any other 

 information which occurs to the collector, such as colouration when fresh, which, 

 is especially desirable if alcohol is used as the preservative fluid. 



