Hybrid sturgeon (Huso husoAcipenser ruthenusAcipenser
gueldenstaedti) in 10x salinity had a lower rate of ammonia excretion and a higher rate of
urea excretion compared to this hybrid in 0x or 5x salinity (Gershanovich and Pototskij,
1995). However, for brown trout, the percentage of nitrogenous waste excreted as urea was
similar in fresh water and in sea water (Dosdat et al., 1997). In R. marmoratus, the
percentage urea excretion decreases with increasing salinity in the range of 0x to 45x
(Frick and Wright, 2002). Blennius pholis also had a lower percentage urea excretion in
sea water than in fresh water (Sayer and Davenport, 1987).