Excess ammonia causes many problems in fish. One significant effect is damage to the gills. Although the most obvious consequence of this is impaired respiration (breathing) this isn't the only problem. Gills are also important for acid-base balance (keeping the pH of the fish's blood correct to allow for normal processes to occur) and ion exchange (keeping the correct amount of important ions such as sodium and chloride in the blood). Thus, damage to the gills prevents a number of important processes from occurring. This leads to extra stresses on the fish as well as an increased potential for infection by bacteria and other invaders.

Ammonia also causes damage to skin, fins and the intestine. More chronic ammonia exposure can cause kidney damage, decreased growth and overall immune suppression. Ammonia also affects the nervous system, resulting in erratic swimming behavior.

What to watch for:
•  gasping/ impaired respiration 
•  abnormal swimming/whirling
•  bloody areas on the body
•  increased mucus production
•  bloody areas in the intestine

•  acute death

What causes excess ammonia?
•  overfeeding 
•  excess leftover food in tank
•  decaying food or animal matter trapped in filter
•  die-off of healthy  bacteria colony due to something like chlorine
•  a tank that was not properly cycled yet and lacks the healthy bacteria needed for the nitrogen cycle

How to decrease ammonia levels in a tank:
•  20% water change two to three times a week (siphon from the bottom of the tank) 
•  make sure you are not overfeeding
•  clean decaying food or animal matter trapped in filter and in gravel
•  add ammonia chips to filter (use only for a temporary emergency fix)
•  use a water conditioner such as Amquel

Thanks to Chuck Dinkel, co-coordinator of the Maryland TIC program, and Lilli Genovesi, NY TIC Coordinator, for this information.