Heavy Metals
Insecticides
Industrial Toxins
Oxygen Depletion

Name of Problem	Probable Cause	Appearance	Species of Fish Affected	More Info
Heavy metal toxicity	contamination of waterways by improperly treated industrial waste	fish in poor condition (long and thin for their age); skeletal deformities, gill and fin abnormalities; tumours	all species
Insecticides	accidental or intentional release of insecticides into water	death (high exposure); other diseases due to inadequate nutrition from affected food chain (lower exposure)	all fish
Industrial toxins	release of improperly treated industrial waste into waterways	varied effects; eye problems, affected fingerlings, poor reproduction and poor survival of stocked fish; mortality	any fish
Oxygen depletion; summer kill or winter kill	lack of oxygen in water	dead fish usually have open mouths and flared, pale gills with no other signs of disease or trauma	all fish; carp and warm water species may be able to survive during low levels of oxygen