The Fish Vet's Blog

In Perth we are fairly lucky with our tap water that it already comes with ~70mg/L of KH (carbonate hardness also known as [the pH] buffering capacity of water). Sometimes a bit more, sometimes a bit less. Provided that we carry out regular aquarium maintenance, we ought not run into issues with pH becoming too acidic because this level of KH should buffer against this. But did you know that this KH will be consumed and decrease over time? When this happens, your pH can fluctuate wildly, causing stress to the fish. Depending on several factors, your pH could drop to as low as 4.5! Very nasty for many fish.

What are some clues that might lead you suspect this could be occurring? Those species intolerant of low pH will develop excess white opaque mucus over their bodies and around the edges of their gill covers. They would become lethargic and hold their fins clamped to their body. The base of Their fins, especially their pectoral and pelvic fins will become congested. Fish will appear disoriented and lose interest in food. You will start to lose fish.

A quick water test would reveal a very low pH. Then a quick KH test would point to the reason for the low pH.

What to do? You will need to act quickly and slowly at the same time. ????

Act quickly to obtain buffering salts. But act slowly in terms of gradually increasing the KH and pH so as not to create more stress in the fish. Speak with your veterinarian or local fish shop for advice on the best combination of buffers for your individual system.

What are common sequelae such a condition? Fish may succumb to secondary bacterial infection and so antibiotics may be indicated.

The bio-filter may be destroyed by the low pH and so you’ll need to treat your system as a “new tank” in terms of the nitrogen cycle.

Also a note of warning whenever you use antibiotics is that it will whack your bio filter around and so it is very important that you conduct daily water testing especially for levels of ammonia and nitrite. Feeding should be reduced while the biofilter re-establishes itself, water changes conducted as necessary and bacteria starter cultures may be indicated at the completion of treatment.

Make sure you get a good set of water test kits.

Very often fish keepers call on veterinarians because they are convinced that they need antibiotics for their sick fish…. after consulting doctor Google. What is the issue with this?

For one thing, antibiotics may not be indicated as the treatment for the condition. There are really very many reasons why fish get sick. Could it be water quality issues? Different parasitic conditions? Virus? Stress? Trauma? Cancer? Notice that GPs do not simply dish out antibiotics at every consultation?

Why not? This paper details a very pertinent reason. High levels of resistance have been reported to amoxicillin, penicillin, tetracycline and oxytetracycline. I concur with this from all the lab testing I have conducted. Where indicated, my first line antibiotic would not include these drugs.

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Zoonotic bacteria, antimicrobial use and antimicrobial
resistance in ornamental fish: a systematic review
of the existing research and survey of aquaculture-
allied professionals
Weir M, A Rajic, L Dutil, N Cernicchiaro, FC Uhland, B
Mercier & N Tusevljak (2012). Epidemiology & Infection,
140 (2): 192 – 206.
Abstract
Using systematic review methodology, global research
reporting the frequency of zoonotic bacterial
pathogens, antimicrobial use (AMU) and antimicrobial
resistance (AMR) in ornamental fish, and human illness
due to exposure to ornamental fish, was examined. A
survey was performed to elicit opinions of aquacultureallied
personnel on the frequency of AMU and AMR in
ornamental fish.
The most commonly reported sporadic human infections
were associated with Mycobacterium marinum,
while Salmonella Paratyphi B var. Java was implicated
in all reported outbreaks. Aeromonas spp. were most
frequently investigated (n=10 studies) in 25 studies surveying
ornamental fish from various sources. High levels
of resistance were reported to amoxicillin, penicillin,
tetracycline and oxytetracycline, which was also in
agreement with the survey respondents’ views.
Studies on AMU were not found in our review. Survey
respondents reported frequent use of quinolones,
followed by tetracyclines, nitrofurans, and aminoglycosides.

Recommendations for future surveillance and
public education efforts are presented

Don’t stress trying to find the nearest veterinarian for your fish. We do house calls on weekends and weekday evenings.

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