PARASITES OF FISHES 51 



common on and in fishes do much damage to their hosts. Their control 

 under natural conditions has never been satisfactorily solved. Many 

 of their life histories have been discovered and usually are found to 

 be very complicated, involving one or more difl^erent hosts besides 

 the fish. Eradication of the parasites would mean the complete ehmina- 

 tion of one of these hosts. This is impractical if not impossible in most 

 of our natural waters because of the great extent and expense involved. 

 Furthermore, some parasites are carried by birds and would soon be 

 reintroduced from other areas. For the time being, it seems that man 

 will have to make the best of the parasite situation, just as fishes have 

 always done. 



