Introduction

Simple and complex cases are presented in an interactive format. It is through case studies that learnings come together. Attendees will realise that if they follow a diagnostic routine, all will be revealed. The next step to solving the problem is to initiate therapy based on the diagnosis and the circumstances.

Case 1

An adult pearlscale goldfish (Carassius auratus auratus) presents with multiple, cystic growths on the skin along its ventrum.

Discussion

It is not an uncommon presentation in this breed. The masses are epithelial lined and filled with clear, colourless fluid. The cysts do not normally pose a problem when small. However, if they become large enough, they can interfere with swimming, or they can tear and predispose fish to infection. Growths can be easily removed without further complication.

Case 2

Koi (Cyprinus carpio) with aeromonad septicaemia are being treated with antibiotics. Based on the antibiotic sensitivity panel, florfenicol was used to treat the fish by intramuscular injection at a dose of 30 mg/kg. All fish reacted adversely to the drug by presenting with diffuse erythema, most apparent on unpigmented parts of the body and fins. Fins are held clamped.

Discussion

Fish were administered with antihistamines, and an alternative antibiotic was used to complete the treatment course. Though most fish do not produce histamines (including the zebrafish, also of the Cypriniformes), zebrafish have homologues for histamine receptors. The antihistamines must have blocked these receptors, explaining why the treatment was effective. Manufacturers of the florfenicol product advised to use a lower dose rate (i.e., 10 mg/kg) in future.

Case 3

In an established, 220-L tank with 3 oscars (Astronotus ocellatus), one started to lose buoyancy control, and when at rest it would be vertical, head down. The other two fish show no signs of illness. What could cause this fish to be ill?

Discussion

Generally, buoyancy issues in many fish can be due to a variety of reasons. It may be related to neural issues (e.g., spinal damage), problems with the swim bladder (e.g., bacterial, parasitic and fungal infections), neoplasia, gaseous distension of the gut, and poor water quality (e.g., low pH, elevated nitrite).

Case 3, Part 2

In this case, it was found that the nitrite levels were markedly elevated on water tests. After quizzing the owner, you realise the owner had changed to a new filter and had inadvertently created "new tank syndrome" in an established tank.

What management and treatment options will you prescribe for nitrite toxicosis? How might the owner avoid this situation in future?

Discussion

The protocol for nitrite toxicosis is:

1.  Perform 30–50% water change using gravel siphon.

2.  Raise the salinity to 5 g/L (using rock salt, sea salt, aquarium salt or pool salt [not table salt or iodised salt]) to competitively inhibit nitrite uptake.

3.  Add bacteria starter culture (available from aquarium shop) to help colonise the biofilter.

4.  Raise the pH to the higher end of optimal range (maintain 7.0–7.5 for oscars) to reduce the toxicity of nitrite.

5.  Increase aeration since nitrite interferes with oxygenation.

6.  Fast the fish for 1 week, then reintroduce food minimally.

7.  Monitor nitrite (maintaining it below 0.5 mg/L by water changes).

The owner will need to be briefed on the nitrogen cycle taking approximately four weeks to establish in a tropical freshwater tank. Some options they have to avoid this situation include substituting the new filter material with the old one during the changeover, or they could run the new filter and the old filter simultaneously for a month before dismantling the old one.

Case 4

A pond with koi was being treated for Argulus using trichlorfon at a rate of 1 mg/L. However, it proved to be ineffective despite several doses. Why? How would you manage the situation?

Discussion

Common reasons for ineffective treatments include under-dosing. Many ponds are odd-shaped, and pond depth may vary over in parts, so it is difficult to determine the actual water volume. Recalculate the water volume and drug required. Other common reasons for lack of efficacy include leaving the UV turned on, which can deactivate chemicals, or leaving charcoal in the filter can adsorb medicines. There may be drug resistance, undiagnosed concurrent disease/s and more. In this case, it was because the pH of the water was high (at 8.2, an effect of the concrete pond), causing organophosphates like trichlorfon to degrade more rapidly. An alternative drug was used. Diflubenzuron was applied at a dose of 0.1 mg/L, repeated on days 14 and 30.

Case 5

A single koi (Cyprinus carpio) presented suddenly with a green, rubbery collar behind its head. Fish was otherwise behaving normally. What is it?

Discussion

It was identified as a collar of cured silicone that had come loose in the pond from around one of the pipes. It was easily removed, and there was no noticeable damage to the fish. If left longer, it would have caused pressure necrosis and led to development of secondary bacterial infection.

Case 6

Two clownfish (Amphiprion ocellaris) housed in a tank were found dead overnight. Fish were found on the tank floor, opercula flared, mouth agape, and pectoral fins stretched forward. What could have happened?

Discussion

It was found that the water temperature rose to 36°C. The fish died from a combination of hyperthermia and hypoxia. Observable signs include warmth of the water, the heater indicator light is continuously in the on position, flared opercula and bleached appearance of the gills. High water temperature is particularly stressful for marine fish since water with higher salinity contains less dissolved oxygen.

Case 7

Goldfish (Carassius auratus auratus) were reared as part of a research project to study the lifecycle of Lernaea. Normally, low numbers of Lernaea should not cause significant mortalities if other conditions are optimal. Routine diagnostics found they were also infested with Gyrodactylus. How would you manage this situation?

Discussion

It is not unusual to find more than one type of ectoparasite causing fish illness. To eradicate the skin fluke but preserve the anchor worms, a targeted approach is necessary. In this situation, the fish were treated with a single dose of praziquantel in-water, at a rate of 5 mg/L.

Case 8

An oranda goldfish (Carassius auratus auratus) is presented because its wen (head growth) has grown over the eyes, and the fish is unable to see. How do you manage the situation?

Discussion

These growths arise from around the head/face and do not invade the eye. The fish is anaesthetized in a bath with alfaxalone at 5–6 mg/L. Taking care not to damage the eyes underneath, a scalpel blade is used to shear off the excess growth. Diluted betadine (1 part betadine: 9 parts saline) is applied topically on the exposed surface, and the fish is given flunixin at 0.3 mg/kg IM.

Case 9

A newly purchased percula clown (Amphiprion percula) was treated for white spot disease with copper sulphate in a hospital tank. Within minutes of application, the fish started to lose buoyancy control and floated to the surface. Why is this, and how would you manage the situation?

Discussion

Copper sulphate is contraindicated in certain fish species, including the clownfish elasmobranchs and Syngnathids. Management involves immediately replacing all the water in the hospital tank with water from the main aquarium, and then running activated charcoal and adding EDTA at a rate of 30 mg/L to remove the copper. The fish recovered almost immediately.

Conclusion

Aquatic animal medicine is always interesting, and treatment/management of cases relies on applying basic principles, as well as "thinking outside the box". Be flexible in your approach, modify as needed, and success follows.