Ammonia
Step-by-step explanation:
The major form of nitrogenous waste that fish and larval amphibians actually excrete is ammonia because it is easily excreted in water
An ammonotelic organism excretes nitrogenous waste as soluble ammonia
Most of the aquatic animals including protozoans, crustaceans, platyhelminths, cnidarians, poriferans, echinoderms, fishes, larvae / tadpoles of amphibians are ammonotelic
The majority of ammonia produced by typical fish species results from amino acid catabolism via specific deaminases or by transdeamination through the combined actions of aminotransferases and glutamate dehydrogenase (GDH) where transdeamination is generally considered to be the major route of ammonia production