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.



Common husbandry-related disorders in fish include toxicities caused by ammonia, nitrites, heavy metals, and poisons introduced into the aquatic system.

Traumatic injury related to capture or aggressive tank mates is another husbandry-related problem.

Figure 6: Lateral line erosion in a blue tang. Note the mild periocular cutaneous ulcers.
Lateral line erosion, or hole-in-the-head syndrome, is a condition resulting in ulceration of the skin associated with the sensory tissue on the head and lateral line of a fish (Figure 6). The cause of this condition is unknown, but it improves by addressing husbandry problems such as improving the diet (feeding natural foods) and correcting water quality problems.

Air embolism, or gas bubble disease, is diagnosed by observing gas bubbles in the fins, gills, and eyes of fish. It is caused by cavitating pumps (usually requires pumps of horsepower or larger) that force oxygen and nitrogen into solution. Cavitation occurs when the pump sucks in air either at the intake (when an air stone is placed near the intake) or through a broken valve.

Malnutrition is another possible contributor to disease. The exact nutritional requirements of most fish are unknown, so an underlying deficiency of certain nutrients may be difficult to detect and may predispose fish to secondary diseases. Conditions such as hepatic lipidosis, emaciation, loss of dorsal musculature, disproportionate bodies (big heads and small bodies), and gastrointestinal disorders (e.g. constipation) are most likely directly related to the diet. Obesity and hepatic lipidosis are associated with a high dietary fat intake. Ideally, fish should be fed a diet identical to their natural diet.


Pet fish are susceptible to bacterial, fungal, and viral infections as well as parasitic infestations. A common husbandry-related cause of infectious disease is failure to quarantine new fish before introducing them to the established system. As a result, outbreaks involving pathogenic organisms occur. New fish should be quarantined in a separate system for four to six weeks before their introduction into an established system with other fish. Monitor fish in quarantine for clinical signs of disease. Consider a broad-spectrum therapy, such as a prolonged immersion with a low concentration of copper (see boxed text titled "Copper treatment") or formalin, as a prophylactic treatment.

Bacterial infections

Bacterial disease is one of the most common causes of aquarium fish mortality. Most pathogenic bacteria are gram-negative aerobes and facultative anaerobes.5,6 Immunosuppression due to stress, poor nutrition, a poor environment, or parasitic infestations often leads to bacterial infections with opportunistic pathogens. Clinical signs may vary but often include lethargy, anorexia, hemorrhages (erythema of the fins, mouth, or vent), cutaneous ulcers, fin rot, ascites, exophthalmia, abnormal posturing, and color change. During postmortem examinations, the kidneys provide the best location for bacterial culture in suspected cases of bacteremia or septicemia. Bacterial cultures are best performed by microbiology laboratories that routinely culture pathogenic bacteria from fish.

Fish with bacterial infections can be treated by placing antibiotics in gelatin diets, giving commercially medicated foods, loading food with the antibiotic, or medicating by stomach tube. Antibiotics can also be delivered by intramuscular or intracoelomic injection or through the water either as a bath (10 to 60 minutes) or prolonged immersion (greater than or equal to 24 hr). Most treatments are empirically derived, but formularies are available to guide antibiotic therapy.1,2,5,6


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