The Fish Vet's Blog

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.

Just as we have beef breeds for cattle, meat breeds for sheep and broiler chickens, there are now steps in selecting for such traits in fish. It’s about time…

Aquaculture
Volume 343, Number 3 (April 2012)
	Quantitative genetics of body weight, fillet weight and fillet yield in Nile tilapia (Oreochromis niloticus)
	Authors:	Bjarne Gjerde, Samuel Bekele Mengistu, Jørgen Ødegård, Harry Johansen, Danilo Soza Altamirano
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 343, Number 3 (April 2012)
	Page Numbers:	117 – 124
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	With the objective of how to best improve fillet weight in Nile tilapia (Oreochromis niloticus) through selection round and gutted body weight and fillet weight were recorded at harvest over four generations (G0, G1, G2 and G3) and from which the following traits were derived: Fillet yield (fillet weight×100/round weight), non-edible part of the fish (NEP=round weight-fillet weight), and non-meat part of the gutted weight (NMP=gutted weight-fillet weight). The round weight was recorded on 42,795 offspring of 327 sires and 422 dams, and the other traits on a random sample of 3361 of the offspring of 277 sires and 359 dams. The fish were reared in net-cages in a lake or in earthen ponds. Selection was performed for harvest weight and fillet yield with an equal relative economic weight (50%) on each trait. The heritabilities for round, gutted and fillet weight, NEP and NMP were all moderate (0.16–0.19) and lower for fillet yield (0.06). The effect common to full-sibs (c2) accounted for a large proportion of the phenotypic variance for all traits (0.11–0.19). The genetic correlation between round weight of fish reared in cages and in ponds was unity (1.00), indicating no genotype by environment interaction for this trait. The genetic correlations between round, gutted and fillet weights were all close to unity, as were the genetic correlations of round and fillet weight with the calculated traits NEP and NMP. The close to unity genetic correlation between round body weight and fillet weight indicates that genetic improvement of one of the traits without achieving a proportional genetic change in the other is difficult or even impossible. This implies that improvement of fillet yield through direct selection is difficult to achieve. Still, based on the current results, fillet yield is expected to increase with increasing body weight, both genetically and phenotypically. However, if increased growth leads to harvest at a younger age rather than higher weight, response in fillet yield may not be observed. Improvement of fillet weight can be obtained through selection for increased round body weight, a more efficient strategy as the trait can be recorded on live breeding candidates and as higher economic weight can be put on this trait instead of on fillet yield.
	Citation:	Bjarne Gjerde, Samuel Bekele Mengistu, Jørgen Ødegård, Harry Johansen, Danilo Soza Altamirano . Quantitative genetics of body weight, fillet weight and fillet yield in Nile tilapia (Oreochromis niloticus). Aquaculture, Volume 343, Number 3 (April 2012), pp. 117-124, <http://ejournals.ebsco.com/direct.asp?ArticleID=45ECB6E82013DB147FA4&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=45ECB6E82013DB147FA4

Just read this from AquaVetMed. There’s something they can put onto the meat to eat up the bad bugs…

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