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:
• acute death
What causes excess ammonia?
How to decrease ammonia levels in a tank: