DISEASES, PARASITES, AND PROBLEMS 53 



them from the usual treatments for external parasites. 

 The free-swimming stage of the anchor worm is sensi- 

 tive to strong salt solutions or long exposure to a 

 formalin solution. The insecticide benzene hexachlo- 

 ride at a concentration of 0.1 p.p.m. of the gamma- 

 isomere used in the water in which the fish are con- 

 tained has been recommended. It is quite toxic to 

 fishes and cannot be highly recommended for use on 

 confined fishes. Relevant to diseases and parasites 

 see also Van Duijn (1956) and NigreHi (1943). Rele- 

 vant to physiology of fishes and habitat requirements 

 see Brown (1957). 



