Two species of freshwater stenohaline fish (channel catfish, Ictalurus punctatus; and goldfish,
Carassius auratus) and four species of euryhaline fish (rainbow trout, Oncorhynchus mykiss;
brown trout, Salmo trutta; striped bass, Morone saxatilis; and Gulf sturgeon, Acipenser
oxyrinchus desotoi) were raised in salinities from 0x to 9x, and then their resting ammonia and
urea excretion were compared. The ammonia excretion of channel catfish, goldfish, rainbow
trout, and brown trout was higher in 9.0x salinity than in the other tested salinities, but
ammonia excretion by Gulf sturgeon and striped bass was lowest in 9.0x salinity. The urea
excretion of goldfish and channel catfish increased with increasing salinity, while that of Gulf
sturgeon did not change and that of all other species decreased. In the higher salinities, excretion
of urea-N as a percentage of the total nitrogen excretion (ammonia-N plus urea-N) increased for
channel catfish, goldfish, and Gulf sturgeon but decreased for the other species. Overall, the
effects of salinity were similar for two stenohaline species, while the euryhaline species were
more variable.
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