One of the first line therapies for sick fish is adding salt to the water at low concentrations. It is also useful at high concentrations as a dip to remove external parasites from the fishes. But how do the fish cope with this?
This paper shows that too much of a good thing causes fish stress.
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Clinical and Physiologic Effects of Sodium Chloride
Baths in Goldfish (Carassius auratus)
Burgdorf-Moisuk A, MA Mitchell & M Watson (2011). J.
Zoo Wildlife Med., 42(4): 586-592.
Abstract
Sodium chloride (salt; NaCl) has been used for
freshwater fish to decrease stress and manage a variety
of disease conditions. Recommendations for dose
and duration vary greatly. The purpose of this study
was to determine the potential adverse clinical and
physiologic side effects of different concentrations of
saltwater baths on goldfish.
Eleven goldfish (Carassius auratus) were used in a
cross-over study to assess the effects of three different
salt concentrations (5, 10, and 20 g/L) on plasma biochemistries
and clinical response. Baseline plasma
chemistries were obtained and analyzed immediately
prior to placing the goldfish into the saltwater bath and
after the fish was removed. A 2-wk washout period was
used in-between each treatment. Significant differences
were found in fish in the sodium (10 g/L, P = 0.007; 20
g/L, P = 0.01), chloride (10 g/L, P = 0.006; 20 g/L, P =
0.001), and alanine aminotransferase (10 g/L, P =
0.002; 20 g/L, P = 0.004) after their exposure to 10 and
20 g/L saltwater. Glucose levels were found to differ
significantly after exposure to all three NaCl concentrations
(5 g/L, P = 0.0009; 10 g/L, P = 0.0001; 20 g/L, P =
0.0005). Clinically, 5 g/L and 10 g/L saltwater baths
were well tolerated by the fish for the duration of the
intended 12-hr treatments, with only one goldfish being
removed during the 10 g/L bath at 7 hr for listlessness.
The average time goldfish spent in the 20 g/L salt bath
was 43 min, with six (54%) of the fish remaining in the
20 g/L salt bath for the intended 60-min treatment period.
The remaining 5 (46%) goldfish were removed
because they became listless or dyspneic. All of the
fish recovered from the treatments without complication.
The results of this study suggest that goldfish tolerate
saltwater baths but that physiologic disturbances
can occur at the higher doses.
