352 



FISH DISEASES 



Diseases of the circulatory system: Diseases of age: 



Ruptured myocardium Senility 



Splenomegaly Unknown and accidental causes: 



Gas embolism Edema 



Internal hemorrhage Fighting 



Diseases of the organs of vision: Jumping out of tank 



Blindness Changes in water temperature and 



chemirstry 



Fortunately most of these ailments will not be encountered in the laboratory. However, 

 there are some rather common ailments generally known under the names of Finrot, 

 Fungus, Bladder disease (which causes the fish to constantly spiral about because of 

 poor equilibration), the "Ich" parasites, mouth diseases, and "fluke" parasites of the 

 liver or intestine. Mouth fungus can sometimes be cured by brushing the mouth of the 

 infected fish with 10% neo-silvol or 2% mercurochrome, 2 to 4 times daily, or by giving 

 them an intense salt treatment of 2-1/2 tablespoons of iodized salt* per gallon of water, 

 decreasing the salt concentration by adding fresh water after 24 to 48 hours exposure. 

 "Ich can be treated by brief immersion of the infected fish in dilute potassium permanga- 

 nate, Acriflavin, or salt.** Also a 1% NaCl solution used at high temperatures (83° F. or 

 more) will tend to eliminate the protozoan parasite cysts (white spots) which reproduce 

 as cysts at the lower temperatures. (See U. S. Fish & Wildlife Serv. F. L. #70) 



Nigrelli (1943) described a total of 10 major factors which contribute to the loss of fish 

 in captivity, listing them as follows: 



1. Crowding: There is an optimum population density for each species, and when 

 fish are crowded beyond this density they tend to kill each other off to re-estab- 

 lish the optimum density (Breder & Coates, 1931). There is also the greater 

 opportunity for the spreading of an infectious disease. 



2. Temperature: The range of tolerance is great providing the change is nnade 

 gradually. Rapid changes in temperature render many fish the more suscep- 

 tible to parasitic infection. Possibly a rapid increase in temperature brings the 

 encysted parasites out into activity while a decrease in temperature may cause 

 them to encyst. 



3. Light: Many larval trematodes are positively phototropic, and fish behavior may 

 be affected by a constant source of strong light. There is an optimum concen- 

 tration for plant and fish, in relation to light. 



4. H-ion concentration: This varies with the species, the optimum for marine fish 

 being around 8 and for fresh-water forms near the neutral (pH 7. 0) level. Most 

 fish aid in controlling the pH of their medium, and few, if any, can tolerate an 

 acid environment. 



5. Specific gravity: An increase in the density of the medium increases the res- 

 spiratory and metabolic rates. Since fishes can tolerate a greater density range 

 than can parasites, this fact is often used in prophylactic and therapeutic mea- 

 sures. 



6. Flow and aeration of water: Chlorine and nitrogen are toxic in certain concen- 

 trations, and even oxygen may be too concentrated and cause gas embolisms. 

 There is an optimum level, different for different fish (e.g. , very low for the 

 Betta) which nnust be maintained. 



* Rock aalt or Turks Island Sea Salt are very good. 



♦* One heaping teaspoonful per gallon of water Is a good concentration to be used for several hours per day over several weeks, 

 if necessary. Sea salt, tock salt. Kosher salt, are all better than iodized table salt. 



