In water of salinities below or above 1 to 4 psu, blood ammonia levels
(measured as TAN) in fish were higher after transport. The high TAN
after transport suggests an increased physiological activity of the fish
during osmoregulation. The accumulation of ammonia nitrogen due to
increased metabolites usually observed in transport water may cause
serious problems to the fish, such as increased oxygen consumption and
heart rate, decreased plasma sodium and alteration of the acid–base
balance (El-Shafey, 1998; Tomasso, 1994). In spite of diffusion of unionized
ammonia being the preferential mechanism of ammonia
excretion in teleosts, there is a branchial exchange system between
NH4
+andNa+ions thatmay becomemore important in an environment
with Na+ ions