| Specific growth rate (SGR), feed conversion ratio (FCR), digestible energy of feed (DE), and resting routine oxygen consumption were determined for two stenohaline (channel catfish Ictalurus punctatus and goldfish Carassius auratus) and four euryhaline (rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, striped bass Morone saxatilis, and Gulf sturgeon Acipenser oxyrinchus desotoi) species after acclimation to four salinities (fresh water, 1.0, 3.0, and 9.0‰). Fish were less than 7-months old at the end of these experiments. For stenohaline species, the highest SGR and most efficient FCR and DE were in fresh water. Three of the euryhaline species had higher SGR and had more efficient FCR and DE in 3.0 and 9.0‰ salinities than in lower salinities. For brown trout, 9.0‰ was above the optimum level for SGR and FCR. Except for channel catfish, oxygen consumption was significantly affected by salinity. Resting routine metabolic rate was minimum in isosmotic water only for rainbow trout and striped bass.; Rainbow trout and brown trout were exposed to Yersinia ruckeri , the bacterial pathogen that causes enteric redmouth disease, and kept in fresh water or salinities ≤9.0‰. Rainbow trout mortality was significantly decreased with increasing salinity. Only 2.3% of brown trout in all salinities died. Bacterial growth was not affected by ≤9.0‰ salinity; however, in vitro bacterial adhesion was significantly reduced as salinity increased.; Channel catfish, goldfish, striped bass, and Gulf sturgeon were exposed to Flavobacterium columnare, the bacterial pathogen that causes columnaris disease. Mortality of fish was reduced significantly in 1.0‰ salinity, and none of the fish died in 3.0 or 9.0‰ salinity. None of the Gulf sturgeon in any salinity died after exposure to F. columnare. Although growth of F. columnare was enhanced in 1.0 and 3.0‰ salinities, in vitro adhesion of bacteria was reduced with increasing salinity, which could explain the lower mortality of fish in 1.0–3.0‰ salinity. |
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