Information available about the effects of salinity on ammonia and urea excretion of
fish is sometimes contradictory, probably because of species-related differences. Some
reviews indicate that the urea is a larger proportion of the nitrogenous waste from marine
species than in freshwater species (Wood, 1993; Jobling, 1994). This is true for the gobiid
species Tridentiger obscurus and Tridentiger brevispinis because of their decreased
ammonia excretion after transfer to sea water, where their urea excretion rate was
unchanged (Kakuta, 1988).