Salting Fish: Something More Than a Flavor Enhancer Sept/Oct 2011

Salting Fish
Something More Than a Flavor Enhancer
Mark A. MItchell, DVM, MS, PhD, Dip. ECZM (Herpetology), University of Illinois
A juvenile Australian
arowana (Scleropages
jardini) was presented
for a history of “something
hanging off the fish”. This
particular fish had recently
been imported from a
captive breeding facility in
Malaysia. There were no other
complaints presented by the
owner, and the husbandry
provided the fish was appropriate. Therefore, my next
step was to determine what
was “hanging off the fish”.
I always perform a physical
examination in a patient
using a two step process. The
first step is to evaluate the
animal’s general demeanor,
locomotion, respiration, and
mentation from afar. There is
a great deal of information to
be gained from examining an
animal before restraining it
4 Sept/Oct 2011
for an examination. I naturally
expect an animal to be more
alert (fight of flight response)
and tachypneic once I have
it in my hands, and I need to
know whether those findings
are masking an underlying
illness or not. In the case
of this fish, the presenting
complaint had no effect on
its ability to move gracefully
through the water, its
mentation, or its respirations
(opercular movements). The
second step to a physical
examination is the “hands
on” component; this allows
one to evaluate the status
and function of the different
systems of the patient. Of
course with fish, this can be
a bit trickier than with most
of our other patients.
When working with fish it
is important to consider the
barrier that water provides.
We take for granted that
examining a terrestrial
patient, such as a dog,
requires no real consideration
regarding the conditions we
examine the patient under,
short of possibly limited light
in an examination room.
To perform a thorough
examination of a fish we must
be able to gain access to
the animal out of its natural
aquatic medium. To do this,
and minimize the discomfort
to the animal, it is best to
anesthetize the patient.
Fortunately, anesthetizing
fish is a straightforward
process. Tricaine methanesulfonate (MS-222) is the
only anesthetic approved
for fish. This anesthetic
is absorbed via the gills,
similar to isoflurane through
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the lungs. This particular
fish was anesthetized for
its examination using an
induction dose of 150 mg/L
(ppm). Induction was smooth
and the animal was ready
for its examination within 5
minutes of being placed in
the anesthetic water. Once
anesthetized, it is important
to keep the fish moist to
minimize any chance for
desiccation. I typically place
the fish on moistened paper
towels and spray anesthetic
water over the fish’s
body and gills during the
procedure to ensure it does
not become light or dry.
While to some the concept
of performing a physical
examination on a fish is
a bit overwhelming, the
approach is similar to any
other species. I always start
the examination from the
head of the animal and work
my way back. The primary
sites to be examined include
the eyes, nares, oral cavity,
operculum and gills, fins,
body condition (evaluating
epaxial muscle condition over
the spine), scales/integument,
abdominal space, and anus
and urogenital openings. This
particular animal weighed
95 grams and was in good
body condition. All systems
checked out normal, with the
exception of the integument.
The structures “hanging off
the fish” were attached to the
integument. These structures
were approximately 8-10
mm in length; there were 9
of them found on the fish
(Figure 1).
A diagnosis of a Lernaea
sp. infestation was made.
For those with experience
working with pond fish,
such as koi and goldfish,
these parasites, also called
anchorworms, burrow
themselves into their host.
They have a unique life cycle
in that the male attaches
itself to the female, becoming
one contiguous structure.
These parasites can be
extracted from the fish using
forceps, similar to removing
ticks. Because of their large
“anchor”, it is not uncommon
that open sores are created.
In this case, 5 g/L ppt
sodium chloride (salt) was
added to the fish’s aquarium
to minimize opportunistic
infections. This treatment
was prescribed for a 10 day
treatment. Because there
is little known regarding the
effect of salt treatment on
arowanas, there was a desire
to evaluate pre-treatment
and 24 hour post-treatment
sodium and chloride levels
in the fish. In addition, the
owner had a desire to have
a complete blood count
(CBC) and plasma biochemistry done.
2011 Sept/Oct
5
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Venipuncture in fish is typically
done under anesthesia. The
author typically collects blood
from the ventral tail vein
(Figure 2) or heart. In this
case, the ventral tail vein was
used. This vessel lies along the
ventral surface of the caudal
vertebrae, and is accessed
at the level of the caudal
peduncle. A 22- to 25-gauge
needle fastened to a 3 ml
syringe can be used to collect
the sample, depending on the
size of the fish. The sample
can be collected using a
ventral approach or a lateral
approach (using the lateral
line as a landmark). Because
this fish weighed 95g, and
it is safe to collect 1 ml/100
grams body weight, 0.6 ml
of blood was collected. A
total of 0.1 ml was used to
run a Critical Care Plus Profile
(Time 0), 0.1 ml was used to
run an Avian/Reptilian Profile
Plus and 0.4 ml was used
to perform the CBC. The
CBC was done using manual
techniques because of the
nucleated erythrocytes and
Table 1. Chemistry profiles for the Scleropages jardini infested with Lernaea sp.
and treated with salt.
Parameter
Avian/Reptilian
Profile Plus
Albumin (g/dL)
1.9
AST (IU/L)
228
Bile Acids (μmol/L)
15
Calcium (mg/dL)
10.4
Phosphorus (mg/dL)
7.4
Total protein (g/dL)
3.9
Globulins (g/dL)
2.0
Glucose (mg/dL)
Critical Care
(Time 0)
Critical Care
(Time 24h)
33
37
89
Potassium (mEq/L)
3.9
3.8
3.9
Sodium (mEq/L)
137
138
140
105
107
Chloride (mEq/L)
Figure 1. Examples of the Lernaea sp.
attached to the arowana.
Figure 2. Collecting blood from the ventral
tail vein of the arowana.
thrombocytes; the results were unremarkable.
The results of the Avian/Reptilian and Critical
Care Plus rotors are found in Table 1.
After 24 hours in the 5 ppt saltwater solution, a
second blood sample (0.2 ml) was collected and
processed using the Critical Care Plus rotor (Time
24) (Table 1). The differences noted in sodium
and chloride between the Time 0 and Time 24
hour samples were both <2.5%; the glucose on
the post-treatment sample was 58% higher than
the pretreatment level. After the 10 day course
of treatment the fish was completely healed, with
no signs of new Lernaea spp. infestations.
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Discussion
Arowanas represent one of the
oldest groups of teleosts. This
group is known as the “boneytongue” fish. There are six
different species of arowanas,
and they are found on four
different continents (Australia,
Asia, Africa, and South America).
The reason these fish are of
interest to scientists is that they
represent one of the few groups
of species that strongly support
the theory of Pangaea, being that
these animals are freshwater fish
and are morphologically similar.
The Asian arowana (Scleropages
formosus) is also of special interest
because of its value; however,
it is illegal to privately own this
species in the US because they are
endangered and restricted for sale
by their CITES listing. It is for this
reason their Australian cousins are
desired as pets in this country.
Lernaea spp. is an interesting
crustacean parasite. It is commonly
encountered in koi and goldfish
ponds in the USA, but is less
common in tropical fish. When
it is seen in tropical fish, such as
this arowana, it is in animals held
in ponds under high densities. In
a closed system, like a pond, the
parasite burden can become high
because the fish cannot escape
them (as in a moving body of
water such as a river). Fortunately,
these ectoparasites are easy
to manage on the fish, as was
described in this case, simply
by removing them. It becomes
more difficult when you have to
treat the environment, similar
to ectoparasites (e.g., fleas) in
domestic mammals. Potassium
permanganate and formalin are
commonly used to treat aquatic
systems infested with this parasite.
Because this animal was housed in
a substrate free aquarium, it was
easier to treat the environment by
emptying the water and drying out
the system.
Salt was used to treat this fish
as a prophylactic. Historically,
veterinarians have been trained to
manage skin lesions in a patient
using topical antibiotics; however,
it is best to limit this practice
to cases where it is considered
absolutely necessary. Being
judicious with antibiotics will help
minimize the likelihood of creating
antimicrobial resistant pathogens
within our environment. It is likely
that this fish would have healed
without any treatment once the
parasites were extricated, but
because scales were removed
when the parasites were extracted,
and fish rely heavily on their
innate immune system, it was
done to limit the potential for
complications. The dose of salt
used (5 g/L) to treat the arowana
is higher than that recommended
by most commercial aquarium
products (3 g/L). Freshwater fish
live in an environment that is hypo
osmotic to them, which requires
them to work hard to excrete
excess fluid. By adding salt to
the water, the physiologic burden
is lowered for the fish. The salt
also serves as an antimicrobial.
The dose used is capable of
desiccating many different types
of bacteria, fungi, and water
molds. While the author routinely
uses this higher dose of salt to
treat fish, there is little available
on the effect of this dose on
fish. Treating fish with salt is not
without its potential harm. The
tolerance of freshwater fish to salt
varies from species to species. At
higher doses salt can desiccate
the fish, leading to dehydration.
Sodium and chloride absorbed
by the fish could also lead to
hypertension and salt toxicosis.
Recently, research done in the
author’s laboratory had shown
that the 5 g/L dose did not
appear to have a negative effect
on goldfish;1 however, there is
no information available for this
treatment on S. jardini. It was
possible using the Critical Care
Plus rotors to measure sodium
and chloride levels before and
after treatment. The difference in
sodium and chloride was < 2.5%,
which is an acceptable variance
for sodium in between samples.1
There was a large difference
(58%) noted in the glucose in
between sampling periods, but
this was attributed to stress of
handling and anesthesia.1
This case should reinforce the
value of an in-house point-of-care
meter and the importance of
serial testing. In this case it was
possible to evaluate the patient’s
response to treatment, allowing
for an adjustment to therapy if
needed. Veterinarians that have
the capability to provide such
close monitoring of their patients
will provide a higher quality of
medical management for their
patients and clients.
Reference:
1. Clinical and Physiologic Effects of Sodium Chloride Baths in Goldfish. Journal of Zoo and Wildlife Medicine, Burgdorff A, Mitchell MA, Watson M, in press
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