Practical Fishkeeping Diploma - Week 4, Day 5

Here's the last lesson of week one of the Practical Fishkeeping Aquarist Diploma. Next week, we cover maintenance and husbandry.

Week 4, Day 5: Diseases with multiple causes

Some disease symptoms can be caused by several different pathogens acting together, or none at all. This makes accurate diagnosis extremely difficult, and often second or third opinions along with educated guesses are involved in treating them.

Dropsy (rarely called ascites) — the retention of fluid in the body cavity, which can be caused through any combination of physical injury, pathogenic, parasitic, viral or bacterial infestation, poor water quality and chronic stress.

Signs: bodily swelling until the fish’s scales start to distend, making it look like a pinecone. The swelling may just be confined around the internal organs, or it may cause the entire fish to swell.

Treatment: broad range antibacterial medications are a start, though this will not work against dropsy caused by non-bacterial factors. 3g/l salt may help with osmotic stress, though this may also cause additional bloating in some fish. Move any infected fish to a separate aquarium, as the cause may be transmittable. Where treatment is ineffective, euthanasia may be needed. The addition of epsom salts may be beneficial in some instances.

Pop eye, also called Exophthalmos — this condition of distended or even prolapsed eyes can be down to bacteria, parasites, virus or fungus infection, as well as dietary and water quality issues. Often occurs after physical injury to the eye.

Signs: gross distention or even prolapse of the eye, possibly with clouding. May be found in tandem with symptoms of dropsy.

Treatment: hard without knowing the underlying cause, but a broad range antibacterial medicine is advised, as is 3g/l salt where possible.

Nutritional diseases

Incorrect feeding can lead to illness, causing premature fish deaths or deformities.

Fatty liver — caused by feeding excessively fatty foods, especially terrestrial foods such as mammal and bird flesh to fish.

Signs: outwardly limited. Fish condition may deteriorate rapidly, and the fish may die. Post mortem examination is required to reveal the problem.

Treatment isn’t an option, but the condition can be avoided by ensuring that fish receive the correct diets at all times.

Vitamin deficiencies — rare with today’s modern foods, but can happen where fish are given stale or incorrect diets.

Symptoms: poor colouring, pop-eye (vitamins A and E), poor growth, kinked spines, bloating, deformities, blindness, fin erosion and bleeding (vitamin C).

Treatment: requires the correct diet to be offered to fish with immediate effect. Deformities will be irreversible.

Intestinal blockage/constipation — incorrect foods can build up in the guts and intestines of fish.

Signs: long, unbroken faeces from the fish, bloating around the stomach and even loss of balance as gas builds up in the digestive system.

Treatment: correct the diet, but also offer food with some indigestible content. Daphnia and Cyclops good. Epsom salts added to food or used as a bath may help to flush fish through.

Genetic and physiological diseases

Some diseases are the result of inherited traits or the natural process of ageing. While these are diseases that cannot be treated, knowing their existence helps avoid misdiagnosis with other disease types.

Birth deformities — often caused by inbreeding, rearing eggs in poor conditions, or vitamin deficiencies. Birth deformities may or may not be problematic or fatal.

Signs: any deformity you can think of, from extra or missing fins, to conjoined fish.

Treatment: none, but prevention by choosing good stock and performing good husbandry will reduce incidences.

Old age/senility — inevitable in all living organisms, and untreatable. Knowing the lifespan of your fish will help diagnosis. Some species may be elderly within 12 months, while others may take decades to reach.

Signs: loss of balance, lethargy, blindness, emaciation, loss of condition, or sudden onset of most diseases listed on these pages.

Treatment: none.


Diseases that can transfer to humans are a risk for any aquarist. Zoonotic infections enter the human body usually via ingestion or broken skin.

Zoonotic diseases risk can be reduced by good aquarium protocols. When working inside tanks, broken skin should be protected through the use of waterproof gloves.

After working on any aquarium, or touching any fish, the aquarist should immediately wash their hands with soap and water, and, if there is any concern of zoonotic infections present, a hand sanitising gel should also be used.

ANY unusual symptoms, including fevers, nausea, skin inflammation, sores or raised bumps on the skin that appear after working on aquaria should be discussed with your doctor.

Disposing of dead fish

Fish should never be flushed down a toilet. Nor should a dead fish ever be fed to another fish in your care — this is how diseases spread.

Though it might seem sentimental, burying fish in the garden risks bodies being dug up and eaten by wildlife — a particular problem if zoonoses are involved.

Sealing fish in polythene bags and disposing of them as domestic waste is the sensible option.

Your retailer may have facilities to have fish taken away and incinerated (thereby destroying any pathogens it was carrying) and this is by far the best option in the very few sites that it is available.

That’s it for week four. Next module: Maintenance and husbandry

Click here for next lesson: Siting an aquarium

How to gain your diploma: Once all the course modules and revision pages have all been posted online, we will open a link to a website that allows you to take your free online exam. If you pass the exam, you will digitally receive your very own Fishkeeping Diploma, to show that you have successfully completed the course, and which is yours to display on the wall near your aquarium, hang in your fish house — or keep somewhere safe where you can take it out and just look at it from time to time.

Note: The Fishkeeping Diploma is not a formal or accredited qualification and should not be confused with the type of diploma presented by colleges, universities and other educational establishments.

Further reading from our sponsors

Diagnosing your fish and treating with API Fish Remedies

API Fish Disease Chart

Guide to fish healthcare