FISH DISEASES 91 



tion ; otherwise we would have more trouble in this direction on account 

 of the large numbers of wild fishes from so many parts of the world being 

 imported for aquarium purposes. 



Leeches. There is a small white leech about T /\ inch long occa 

 sionally introduced with living food (daphnia), more particularly in the 

 spring. This attacks the bodies and gills, and if the fish is only a few 

 weeks old the results are fatal. In an aquarium it is easily possible to 

 see them on the glass and the breeder should be on the 'lookout for them. 

 If any are discovered the fishes should be carefully removed to an 

 aquarium where they can be kept under observation. The aquarium 

 should be disinfected by ammonia (page 102). These and larger leeches 

 can be removed from the gills of larger fishes by the injection of strong 

 salt water, or by the progressive salt water treatment previously described. 



Fish Lice. While not very common, and seldom if ever fatal, this 

 crustacean parasite is very annoying. It is about }i inch in diameter, 

 very flat, of a nearly rounded outline and is quite translucent, but dis- 

 tinctly showing handsome iridescent colors under a good magnifying glass. 



Fig. 70. Fish Louse. Argulus (Enlarged four diameters) 



They are free swimmers and are able to hold most tenaciously to their 

 hosts. So tight is their hold that even after death by poisoning they 

 still adhere where fastened. Owing to their translucent quality they are 

 difficult to see. The fishes will scratch themselves much the same as in 

 cases of the "Itch," but one can notice small irritated spots, particularly 

 on the fins. The body, however, is not free from attack. The lice adhere 

 tightly, but can be scraped off with the point of a knife. 



Treatment consists in the use of permanganate of potash, the strength 

 varying according to conditions. If there is much organic matter present, 

 such as leaves, settlings and green water, the strength may be made as 

 high as J / 2 grain by weight to the gallon of water, especially in a wooden 

 tank. If the container is very clean and there is nothing in it except the 

 fishes, }i grain per gallon is enough. In general, T /\ grain per gallon is 

 safe. Unless the fishes show signs of dying, the water does not need to 

 be changed, as most of the chemical expends its strength within an hour 

 and clears in a few days. 



As the treatment does not affect the eggs of the parasites, a second 

 application should be given in a week, especially in ponds or pools. 



Flukes. The detection of flukes is not easy without the aid of a 

 microscope, the cause being a small parasite worm (Gyrodactylus elegans), 

 chiefly infesting the gills. The fish breathes unnaturally fast, frequently 



