566 EXPERIMENTAL FISH EMBRYOLOGY 



Non-parasitic and non-lnfectloua dlaeasea . 

 Diseases of the digestive system: 



Liver degeneration 



Biliary cirrhosis 

 Diseases of the reproductive organs: 



Egg bound 



Ovarian degeneration 

 Diseases of the circulatory system: 



Ruptured nyocardlum 



Splenomegaly 



Gas emboli am 



Internal hemorrhage 

 Diseases of the organs of vision: 



Blindness 

 Diseases of the skeleton and organs of locomotion: 



Swim bladder trouble 



Lordosis 

 Diseases due to nutrition: 



Malnutrition 

 Diseases of age: 



Senility 

 Unknown and accidental causes: 



Edema 



Fighting 



Jumping out of tank 



Changes in water temperature and chemistry 



Fortunately most of these ailments will not be encountered in the laboratory- How- 

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

 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 flah 

 with 10^ neo-silvol or 2^ mercurochrome, 2 to 1+ times daily, or by giving them an Intense 

 salt treatment of 2^ tablespoons of iodized salt per gallon of water decreasing the salt 

 concentration by adding fresh water after 2l+ to kQ hours exposure. 'Ich" can be treated 

 by brief Immersion of the infected fish in dilute potassium permanganate, or Acriflavln. 

 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 tempera- 

 tures. 



Nigrelli (19'^5) 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-establish 

 the optimum density (Breder & Coates, 1951)- There la also the greater opportun- 

 ity for the spreading of an infectious disease. 



2. Temperature : The range of tolerance is great providing the change is made gradu- 



ally. Rapid changes In temperature render many fish the more susceptible to 

 parasitic infection. Possibly a rapid increase in temperature brings the en- 

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

 them to encyst. 



5. Light : Many larval trematodes are positively phototroplc, and fish behavior may 

 be affected by a constant so^lrce of strong light. There Is an optimum concentra- 

 tion for plant and fish. In relation to light. 



h. H-lon 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 environnient. 



