Common Environmental Hazards for Fish
Environmental Hazard | Problem | Behavioral Clinical Signs | Physical Clinical Signs | Acute Mortality | Chronic Mortality |
|---|---|---|---|---|---|
Low dissolved oxygen | Hypoxia | Piping at surface; large fish affected more than small ones | Flared gills, dark | Catastrophic mortality | Ongoing |
Temperature fluctuation | Power failure, thermostat failure | Evidence of infection, sudden death | Immune compromise; depends on infectious agent | Yes | Possible |
Gas bubble disease | Supersaturation (often N2 gas) | Lethargy, buoyancy problems | Gas bubbles in gill capillaries, fins, and eyes; exophthalmos (“popeye”); fine gas bubbles may be visible along the glass inside an aquarium | Catastrophic mortality | Ongoing |
Carbon dioxide toxicity | CO2 > 40 mg/L | Lethargy at surface | None | Yes | Yes |
Ammonia toxicity (new tank syndrome) | Un-ionized ammonia > 1 mg/L pH > 8 | Lethargy, anorexia, spinning, convulsive swimming | Darkened | Catastrophic mortality | Ongoing |
Nitritea toxicity | NO2 > 0.1 mg/La Low chloride (freshwater) | Piping at surface | Gills and blood dark brown color, although this can be difficult to discern | Yes | Yes |
Nitrateb toxicity | NO3 –N ≥ 70 mg/L Low (no) iodine, O3 | Lethargy | Swelling around throat (thyroid hyperplasia/"goiter") | No | Yes |
Old tank syndrome | Total alkalinity (TA) ~0 mg/L pH < 6, high total ammonia nitrogen (TAN) | Lethargy, poor appetite | None | No | Yes |
Lack of minerals | Total hardness < 20 mg/L Use of distilled water | Sudden death | None | No | Yes |
Chlorine toxicity | Detectable chlorine (caveat: in some acute cases chlorine may not be detected after an event) | Acute: sudden death Chronic: lethargy, irritation | Acute: none Chronic: excess mucus, cloudy eyes, gill inflammation/ necrosis | Catastrophic mortality | Ongoing |
Hydrogen sulfide toxicity | Detectable H2S (rotten egg smell) | Acute: sudden death Chronic: lethargy, poor appetite/growth | None | Catastrophic mortality | Ongoing |
Copper toxicity | Cu2+ > 0.2 mg/L Low alkalinity | Sudden death | None | Catastrophic mortality | Ongoing |
Zinc toxicity | Coins in pond Stainless steel, acidic pH | Lethargy, anorexia | None Enlarged abdomen (coins in GI tract) | Not usually | Yes |
Stray voltage | Electrical short, mechanical problem | Irritation, mortality | Fractured spine | Yes | Yes |
a There is tremendous species-specific variation to nitrite toxicity. Environmental conditions, especially chloride concentration, can mitigate the effects. Most test kits measure mg/L NO2−N. To convert to NO2 (mg/L) concentration, this value must be multiplied by 3.3. b Most test kits measure mg/L NO3−N. To convert to NO3 (mg/L) concentration, this value must be multiplied by 4.4. | |||||