ISRAEL JOURNAL OF
VETERINARY MEDICINE
SOME BLOOD PARAMETERS IN THE EEL (ANGUILLA
ANGUILLA) SPONTANEOUSLY INFECTED WITH
AEROMONAS HYDROPHILA
1
Yavuzcan Yildiz H., 1Bekcan S., 1Karasu Benli A. C. and 2Akan M.
Vol. 60 3) 2005
1. Ankara University, Faculty of Agriculture, Dept. of Fisheries and Aquaculture,
06110, Diskap•, Ankara, Turkey
2. Ankara University, Faculty of Veterinary Medicine, Dept. of Microbiology,
06110, Diskap•, Ankara,Turkey
Aeromonas hydrophila causes a haemorrhagic septicaemia in fish (1, 2, 3).
Most cultured and feral fishes such as brown trout (Salmo trutta), rainbow
trout (Oncorhynchus mykiss), Chinook salmon (Oncorhynchus tshawytscha),
ayu (Plecoglossus altivelis), carp (Cyprinus carpio), clariid catfish (Clarias
baatrachus), Japanese eel (Anguilla japonica), American eel (Anguilla
rostrata), gizzard shad (Dorosoma cepedianum), goldfish (Carassius auratus),
golden shiner (Natemigonus crysoleucas), snakehead fish (Ophicephalus
striatus) and tilapia (Tilapia nilotica) are susceptible to A. hydrophila infection.
(1, 2, 4).
A. hydrophila had previously been reported from eel (Anguilla anguilla) in
Turkey (5). However, an analysis of the changes in the haematology of eel
infected by A. hydrophila has not been conducted so far. The objective of this
study was to assess the changes in certain blood parameters following
spontaneous infection of eel (Anguilla anguilla) in order to evaluate the
haematological changes due to the disease.
Clinical signs including haemorrhages with dermal ulcers were observed in
eel during the adaptation period to artificial feed. Out of 24 fish, ten showed
these signs. For microbiological examination, materials obtained from internal
organs and muscle lesions were inoculated onto MacConkey agar (Oxoid
London, UK) and brain heart infusion (BHI, Oxoid, London, UK) agar
containing 7% sheep blood. All plates were incubated in air at 20-25oC for 24
h. The bacterium isolated was identified as A. hydrophila. Three days after
observing the first signs, blood parameters were analyzed from affected fish.
Healthy eel (control), not exhibiting signs and from which bacteria were not
isolated served as negative controls. A total of 20 fish were examined. Eel
exhibiting signs of the disease (N=10) and healthy (N=10) fish obtained from
different aquaria (70x40x50 cm) in the same unit were examined. The fish
weighed around 150 g. Water temperature was 26±1oC in the tank containing
the infected fish. The dissolved oxygen was about 6.5 mg/l and pH was 7.8.
Fish were initially fed with white worm (Enchytraeus albidus) at a restricted
level then with commercial trout diet (40 % crude protein) at a daily rate of 2%
of their body weight. There was no filtration system in the tanks. Tanks are
cleaned daily by siphoning.
Blood was collected by cardiac puncture using heparinized syringes. Blood
plasma was obtained by centrifugion at 1500 g for 15 min and stored in plastic
screw top tubes at -18oC until analyses. The plasma obtained from each of
two fish was pooled. Hematocrit measurements were made by drawing wellmixed samples of blood into heparinized capillary tubes and centrifuging at
12500 rpm for 4 min (6). Total plasma protein was measured by the Biuret
reaction as described by Siwicki and Anderson (6). Plasma Na+ and K+ levels
were determined (Teco, Anaheim, California, USA), plasma glucose, Mg++,
Ca++ and Cl- were determined (Clonital, Carvico, Italy) with a Schimatzu UV1200 UV spectrophotometer.
Statistical analysis was performed by Student’s t test. Mean differences
with p<0.05 were considered statistically significant.
Table 1 shows the results of the blood analysis of spontaneously infected with
A.hydrophila compared with clinically healthy eel. The following differences
were found (a) significant reduction (p<0.01) in hematocrit, total plasma
protein, Na+, Cl- in infected eel; (b) significant increases (p<0.01) in the
plasma glucose and K+ in infected eel; (c) unchanged values (p>0.05) of
Mg++ and Ca++. Post-mortem examination showed haemorrhages of the skin
associated with superficial ulcers (Fig 1). The cumulative mortality reached
30% over four days.
The data emphasize the considerable hematological changes which take
place in eel following spontaneous infection with A. hydrophila. No study was
available to compare alterations of blood value in eel experimentally infected
with A. hydrophila, however, the pattern of changes was, in general, similar to
that observed in other bacterial infections (7, 8, 9). In this study a reduced
hematocrit was detected in diseased fish. Thus, hemopoiesis may be severely
affected in bacterial diseases (7). Also,total plasma protein decreased
following A. hydrophila infection. This finding is in agreement with previous
reports (7, 8, 10, 11, 12). The electrolyte balance was disrupted with respect
to Na+, Cl- and K+ after infection. The decreased levels of electrolytes except
Ca++ and Mg++ are possibly related to the increased permeability of the renal
tubules whereby electrolytes are excreted in excess in the urine (7). Increased
plasma K+ may be interpreted as an indication of the response of intracellular
acid-base balance due to pathological stress (13). Plasma glucose levels
were elevated in this study. High levels of glucose were also reported for
brook trout infected with Aeromonas salmonicida (10).
Outbreaks of disease are usually associated with changes in the
environment. Stressors including overcrowding, high temperature, a sudden
change of temperature, rough handling, transfer of fish, poor nutritional status
contribute to physiological changes and exacerbate susceptibility to infection
(4). In the present study the fish showed inappetance for the artificial feed.
Considering the impaired nutrition of eel due to failure to feed, the emergence
of the disease could be attributed to starvation stress. Thus, motile
aeromonas infection in fish is a classic example of a stress-borne disease
(14).
Figure 1. Skin haemorrhages and superficial ulcers of the eel (Anguilla anguilla) infected with
Aeromonas hydrophila
LINKS TO OTHER ARTICLES IN THIS ISSUE
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