Adaptations of Fishes 185 



These alkaloids are most developed in the ovaries and testes, 

 and in the spawning season. They are also found in the liver 

 and sometimes elsewhere in the body. In many speeies other- 

 wise innocuous, purgative alkaloids are developed in or about 

 the eggs. Serious illness has been caused by eating the roe of 

 the pike and the barbel. The poison is less virulent in the 

 species which ascend the rivers. It is also much less developed 

 in cooler waters. For this reason ciguatera is almost confined 

 to the tropics. In Havana, Manila, and other tropical ports it 

 is of frequent occurrence, while northward it is practically un- 

 known as a disease requiring a special name or treatment. On 

 the coast of Alaska, about Prince William Sound and Cook Inlet, 



Fig. 139. — Numbfish, Narcine hrasiliensis Henle, showing eleiiric cells. 

 Pensacola, Florida. 



a fatal disease resembling ciguatera has been occasionally pro- 

 duced by the eating of clams. 



The purpose of the alkaloids producing ciguatera is con- 

 sidered by Dr. Pellegrin as protective, saving the species by the 

 poisoning of its enemies. The sickness caused by the specific 

 poison must be separated from that produced by ptomaines and 

 leucomaines in decaying flesh or in the oil diffused through it. 

 Poisonous bacteria may be destroyed by cooking, but the alka- 

 loids which cause ciguatera are unaltered by heat. 



It is claimed in tropical regions that the germs of the bu- 

 bonic plague may be carried through the mediation of fishes 

 which feed on sewage. It is suggested by Dr. Charles B. Ash- 



