Ammonia is the major end product in thebreakdown of proteins in fish. Fish digest the protein in their feed and excreteammonia through their gills and in their feces. The amount of ammonia excreted by fish varieswith the amount of feed put into the pond orculture system, increasing as feeding ratesincrease. Ammonia also enters the pond from bacterialdecomposition of organic matter such asuneaten feed, dead algae and aquatic plants.