Laboratory techniques

image of Laboratory techniques
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Clinical signs exhibited by unhealthy fish are common to many diseases and pathological conditions. These signs are frequently limited to lethargy, anorexia and colour changes. This chapter opens discussion on water quality, clinical examination, postmortem examination, ectoparasite examination, blood sampling, bacteriology, parasitology, histopathology, mycology and virology.

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Figure 13.1 Some simple affordable test kits for monitoring water quality, based on the use of (from left to right) a dry tablet, liquid reagent, impregnated dipstick and dry powder reagent. (© W.H. Wildgoose.)
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Figure 13.2 Multi-parameter ion-specific photometers are accurate and, for portability, some can operate on a 9 volt battery. The instrument is set to zero with a water sample, then reagents are added to produce a colour change that is measured by a photocell. (Courtesy of Hanna Instruments.)
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Figure 13.3 Portable dissolved oxygen meters can be calibrated in air for a percentage saturation value or in zero-oxygen solution for a measurement in milligrams per litre. The selective membranes that cover the polarographic probe require periodic replacement. (Courtesy of Hanna Instruments.)
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Figure 13.4 Salinity can be measured to varying degrees of accuracy, using (from left to right) a ‘swing-needle’ hydrometer, a floating hydrometer, a conductivity meter and a refractometer. (© W.H. Wildgoose.)
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Figure 13.5 The lateral body wall of a male goldfish is removed to expose the internal organs during a postmortem examination. The pericardial sac is opened to reveal the heart (arrowed). (© W.H. Wildgoose.)
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Figure 13.6 The gonad is reflected ventrally at the cloaca and the liver is resected to expose the bowel and white bilobed swim-bladder (arrows). The latter can be removed to allow more access to the posterior kidney situated on the dorsal aspect of the body cavity. (© W.H. Wildgoose.)
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Figure 13.7 A skin scraping is taken from behind the pectoral fin, using a blunt scalpel. A small sample of opaque mucus is visible on the blade. (© W.H. Wildgoose.)
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Figure 13.8 The mucus is transferred to a microscope slide and mounted with a drop of tank/pond water and a glass cover slip. (© W.H. Wildgoose.)
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Figure 13.9 A skin fluke is visible under low-power magnification (×40 original magnification) among the cell debris and mucus. Most microscopic ectoparasites are motile, refractile to light and more visible with phase-contrast or a low condenser setting. (© W.H. Wildgoose.)
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Figure 13.10 A gill biopsy is taken, using fine scissors to sample the tips of several gill filaments. (Reproduced with the permission of .)
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Figure 13.11 The filaments are separated in a drop of tank/pond water and a cover slip is applied lightly. (Reproduced with the permission of .)
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Figure 13.12 A severe infestation of motile gill flukes is visible between the gill filaments under low-power magnification (× 40 original magnification). (© W.H. Wildgoose.)
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Figure 13.14 Taking a blood sample from the caudal vein of a koi using a lateral approach. A long needle is inserted under the scales of the peduncle at a point on or just below the lateral line (arrowed). (© W.H. Wildgoose.)
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Figure 13.15 A bacteriological sample is taken using a sterile loop inserted into the posterior kidney of a koi. Care must be taken to avoid accidental contamination of the site during exposure of the organ. (© W.H. Wildgoose.)
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Figure 13.16 Culture plates are inoculated by ‘plating out’ to thin out the sample, using a series of three to four short strokes with a sterile loop.
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Figure 13.17 The API test system for identification of bacterial organisms. The lower strip is unused; the middle one has been inoculated with and the top with . (© W.H. Wildgoose.)
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Figure 13.18 Antibiotic sensitivity test with showing resistance to six out of eight antibiotics. Bacterial resistance to multiple antibiotics is common. (© W.H. Wildgoose.)
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Figure 13.19 The minimum inhibitory concentration (MIC) determined using the ‘E-test’. Here, a minimum concentration of 0.047 μg of ampicillin per kilogram bodyweight is required, to be effective against this strain of from a goldfish. (Courtesy of G. Barker.)
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Figure 13.21 Normal histology of the posterior kidney from a koi. There is a substantial amount of normal haemopoietic tissue present in the interstitial tissue. This is occasionally misinterpreted as neoplastic by those not experienced in fish pathology. H&E stain, ×100 original magnification. (© W.H. Wildgoose.)
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Figure 13.22 Thyroid follicles (arrowed) in the anterior kidney of a koi. In carp and goldfish, some thyroid tissue is found in many organs, including the heart, spleen and posterior kidney. H&E stain, ×100 original magnification.
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Figure 13.23 Hepatopancreas of a carp. The distinctive pancreatic tissue (arrowed) contains large eosinophilic zymogen granules and surrounds a blood vessel. H&E stain, ×100 original magnification. (© W.H. Wildgoose.)
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Figure 13.24 Packaging and cooling blocks for the submission of samples for virology. Various samples may be required, including some in (from left to right) neutral buffered 10% formalin, glutaraldehyde and transport medium. A courier service may be required to deliver the samples within 24 hours. (© W.H. Wildgoose.)
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