Performing a basic examination in fish - Veterinary Medicine
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Performing a basic examination in fish
You have the skills to care for fish, so take the opportunity to accept these aquatic creatures as patients. Be sure to explore husbandry issues, since inappropriate care is often the underlying cause of many disorders in fish.


Figure 2: Scraping the skin of a koi to obtain mucus with a microscope slide.
Blood samples are collected for complete blood counts, serum chemistry profiles, and toxicology screens. For the best results, perform hematologic evaluation immediately by using your in-house laboratory, but other testing can be performed by commercial laboratories.

Coelomic fluid can be collected by aspiration in fish with dropsy. The fluid sample is evaluated in the same manner as abdominal fluid in mammals; that is, evaluate cellular and protein content and perform a microbial culture.

Figure 3: A fin clip biopsy performed on a koi.
Obtain a mucus smear by pressing a clean microscope slide onto the surface of a lesion or by gently scraping the skin with the edge of the slide in a cranial to caudal direction (Figure 2). Examine the mucus smear as a wet mount with a drop of tank water. In general, microscopic evaluation of mucus smears are performed to detect parasites, fungi, and bacteria.

Figure 4: A gill biopsy performed by using fine-tipped scissors inserted under the operculum of a koi.
Obtain a fin biopsy sample by using fine-tipped scissors to remove a triangular wedge of fin tissue, ideally between the fin rays (Figure 3). Evaluate the sample as a wet mount under a coverslip. Microscopic examinations of fin samples are used to detect ectoparasites, fungi, and bacteria.

Figure 5: A wet mount of a gill biopsy sample revealing focal epithelial hyperplasia and excessive mucus production associated with a trichodinid parasite (100X).
After opening the operculum, obtain a gill biopsy sample by using fine-tipped scissors to remove a few tips of primary gill lamellae (Figure 4), and examine it as a wet mount. Gill biopsy samples are evaluated microscopically to assess gill damage, such as hyperplasia and hypertrophy of epithelial cells and increased mucus production that can compromise gill function (Figure 5). Gill injury commonly occurs with bacterial or parasitic infections or with poor water quality.

Obtain a fecal sample by inserting a swab or small loop through the vent and into the intestine or by collecting feces as they pass from the fish. A fecal sample is also examined as a wet mount. Microscopic examination of feces is used to detect parasite ova or potentially pathogenic protozoa.


Copper treatment
Isolate sick fish, especially those suspected of having an infectious disease, from other fish in a separate aquatic system until they have recovered. Consider a broad-spectrum therapy, such as a prolonged immersion with a low concentration of copper (see boxed text titled "Copper treatment") or formalin, during the quarantine period. Provide specific treatment of fish in quarantine exhibiting parasitic, fungal, or bacterial infections once a diagnosis is made.


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