Except for the Gulf sturgeon, all of the euryhaline species in the present study had
decreased urea-N excretion with increasing salinity, both as absolute values and as the
percentage of total nitrogen excretion, but had variable changes in ammonia-N excretion.
Most of the previous studies of the effect of salinity on excretion of nitrogenous waste
compared fish in fresh water and sea water (Sayer and Davenport, 1987; Kakuta, 1988;
Dosdat et al., 1997), which may not be applicable to the present study. R. marmoratus in
15x salinity, compared to fresh water, had increased ammonia excretion and a decrease in
the proportion of nitrogenous wastes excreted as urea (Frick and Wright, 2002). Gulf
sturgeon in 9xsalinity (present study) and hybrid sturgeon in 10xsalinity (Gershanovich
and Pototskij, 1995) had similar trends, compared to freshwater controls, in ammonia-N
excretion and percentage of nitrogenous wastes excreted as urea.