AP BIOLOGY

Detailed explanation-1: -Ammonia is the excretory waste in fishes. It is easily soluble and hence, is excreted by simple diffusion process across body surface or through their gills.

Detailed explanation-2: -Freshwater fish mostly excrete ammonia with only a small quantity of urea. It seems the ornithine cycle for urea production has been suppressed in all freshwater teleosts except for some airbreathers which, when exposed to air, increase urea synthesis via the cycle.

Detailed explanation-3: -The gills are the primary site of ammonia excretion in fish (Wilkie, 1997, 2002; Weihrauch et al., 2009), because they have large surface area, perfusion by 100% of cardiac output, large ventilation rates, small diffusion distances, and contact with a voluminous mucosal medium (Evans et al., 2005).

Detailed explanation-4: -Ammonia is the primary excretory product in animals, it is derived from the proteins present in the food we eat. It is the most toxic nitrogenous waste and is excreted by diffusion by most of the amphibians and aquatic animals. Mammals excrete nitrogenous waste as urea.

Detailed explanation-5: -Ammonia accumulates easily in aquatic systems because it is a natural byproduct of fish metabolism. All animals excrete some waste in the process of metabolizing food into the energy, nutrients, and proteins they use for survival and growth. In fish, the principal metabolic waste product is ammonia.