DISEASES, PARASITES, AND PROBLEMS 45 



be acclimated to the new temperature. In most situa- 

 tions this can best be accompUshed by placing fish in 

 a plastic bag partly filled with water from their origi- 

 nal container and then placing the bag in the tank to 

 which the fish are to be transferred. After the tem- 

 perature of the water in the bag has reached the 

 temperature of that in the tank, the fish may be re- 

 leased. If the fish are too large or numerous, cooler or 

 warmer water may be added to the old tank over a 

 one-hour period to bring it to the temperature of the 

 new container. 



Fighting 



Fishes confined in tanks are frequently killed or 

 damaged by fighting. Fighting may occur either be- 

 tween species or between members of the same spe- 

 cies. Fighting between members of the same species 

 is much more common in some species than in others. 

 Size difference encourages fighting, and there is little 

 doubt that seasonal sex activity also plays a part. An 

 aggressive fish can kill another of equal size by con- 

 stantly nipping and bumping it. This is very evident 

 in the sunfishes. A predaceous form such as the 

 largemouth bass will often kill small fish over and be- 

 yond what it uses for food. 



Viral Diseases 



Viruses cause a number of diseases of fishes but 

 we have knowledge of only two or three of these ail- 

 ments. Lymphocystis is easily recognizable but does 

 not cause heavy mortahty and is of questionable im- 

 portance among captive fishes. Lymphocystis infects 

 the epidermis of fishes where it causes hyperplasia 



