Photos by Dr. Gerald Bassleer

Diseases Common Among Almost All Cichlids


What are they? Spironucleus are small (size 10μ [micrometers] or 0.01 mm) flagellates (one-cellular organisms with a flagella) that can often be found in small quantities in the intestinal tract of cichlids.

Did you know? They were recently identified as Spironucleus and not as Hexamita.

CAUSES: These parasites can become a serious infection when stress conditions such as bad handling, poor packing, overcrowding, unbalanced or poor food quality, aggression, etc. are having a negative impact on the fish and its immune (defense) system is weakened.

COMPLICATIONS: Also, other infections (i.e. bacterial infections or intestinal Nematode worm infections) can trigger this internal, parasitic infection.

TRANSMISSION: Adult fish can pass on this parasitic infection to their babies.

NOTE: When examining the organs of the fish, we have to be careful not to confuse these with sperm of male cichlids.

CLINICAL SIGNS (SYMPTOMS): These vary from case to case and are not always typical.

  • Darkening coloration of the fish
  • Listlessness
  • Lack of appetite
  • At an advanced stage, after several days or weeks, the fish will look emaciated, and slimy excrement will be hanging out of typical anus.
  • Secondary bacterial infections can occur. At this stage, there may be mortality (deaths).
  • After several weeks or months, certain adult fish like discus or uaru will exhibit holes in the head region and erosion of the lateral line (also called HLLS = Head-and-Lateral-Line-Syndrome or HITH = Hole-in-the-Head-Syndrome).

Slimy excrement hangs out of the anus of this astronotus with a Spironucleus infection

TREATMENT: The sooner you can start with an adequate treatment the less damage (fewer mortalities) will occur. Fish that had HLLS or HITH can still have scars (i.e. holes) after successful treatment. Use a food with good algae or herbs (prebiotics) such as Biofish Food Chlorella or Biofish Food Green.

In the early stages, food with phytobiotics such as Biofish Food garlic (the only one with fresh, uncooked garlic) can help the fish control the infection.

In more advanced stages, continue with Biofish Food garlic and add Metronidazole (500-750 milligrams or mg per 100 liters or L of aquarium water) or commercial products like Hexamor (Aquarium Münster) over 36-48 hours. You can raise the temperature by 3°C during the treatment; this increases the speed of the cycle of the parasite and activates the physiology of the fish.

When fish are still eating, you can try to add 500 to 750 mg Metronidazole in 100 grams or gm fish food, but most fish will not like the taste. Note that young fish do not tolerate Metronidazole well.

In the advanced stages of infection, you might need to add an anti-bacterial (i.e. Furaltadone or Nitrofurantoin) to control the secondary, internal bacterial infections.

PREVENTION: Preventative measures including good care and avoiding stress are recommended.


What is it? Mycobacterium is a bacterium (gram positive) that usually grows in the organs or muscular tissue of the fish, most likely seen as tubercles. It shows up as an infection or disease after many months or years.

WHERE IT FLOURISHES: The environmental conditions for these bacteria are favorable in our aquaria (and ponds): tropical and consistent aquatic habitat, usually permanently polluted, that is similar to an incubator. Usually these bacteria are introduced by other fish or through fish food (i.e. mosquito larvae, also frozen). The female parent fish already passes on Mycobacterium via the eggs so the babies could become carriers of fish tuberculosis.

CLINICAL SIGNS: This infection is mostly common in older cichlids and is therefore also called ‘old age syndrome’.

  • Loss of color
  • Emaciation and slowly wasting away
  • In some cases, they show ulcers
  • Fish that are only several months old can have serious infections with signs like discoloration, swollen belly, pop-eye (exophthalmos), fast respiration, and ulcers.

TREATMENT: Here, it is important to understand that “an ounce of prevention is better than a pound of cure.” Use mosquito larvae free of Mycobacterium; use brood stock that is free of the bacterium. Many of us tried several antibiotics but there is actual no cure for this infection.

We recommend separating infected fish and to help the remaining fish fight off the infection by giving them a clean aquatic environment (this means also cleaning filters) and a fish food with beta-glucans that stimulates their defense (immune) system (i.e. Biofish Food forte).


Species-Typical Diseases


Massive gill flukes in a fish’s gills, magnified 200x

CAUSE: There are many different kinds of gill flukes (monogenetic Trematodes) that infect angel fish and discus. The most common is Dactylogyrus (size 0.3-0.5 mm); it is found in tank- or pond-raised fish since the parasite is not easy to control.

The worms lay eggs that hatch after 7 to 21 days and the infection is not noticeable in the first stage of the disease. Usually we see very few worms (only 1 or 2 on each gill arch), but when fish are kept in poor and overcrowded conditions, this can become a serious infection within one week.


  • In the first stage, the fish shows respiration problems, sometimes scraping against objects.
  • Young fish quickly exhibit secondary bacterial infections, become listless, and die much sooner than older fish.
  • Older fish suffer from emaciation, listlessness, opened gill covers, a loss of color, and a lack of appetite.

TREATMENT: Try to treat this worm infection during its early stages. If you wait too long, there will be too many eggs infesting the pond or aquarium. You will need not just one but three treatments at intervals of seven days to control this parasitic worm infection.

Most commonly used over the last decade to treat this infection is Praziquantel at 250mg/100L (i.e. Dactymor by Aquarium Münster). Another recommended medication is Flubendazole 100-200mg/100L. Salt or formalin is, in most cases, ineffective for total control of the infection.

Make sure that you clean, siphon, and medicate the filter since worm eggs can be found there. Also, siphon the bottom of the aquarium.


You can see the small holes in the nose region of this discus

What is it? HLLS or HITH is a syndrome and cannot be called a disease because a specific pathogen or specific cause of this disorder cannot (yet) be identified. It is mostly noticed in adult discus and uaru but is also found in:

  • Astronotus
  • Heros
  • Mesonauta
  • Varieties of geophagus
  • African cichlids can also show similar signs
  • This syndrome is also known among certain marine fish like tangs and angel fish


  • It usually starts with a few, small holes in the nose region
  • Later, these will be found on the head and the lateral line on the side of the body. The ‘lateral line’ organ extends all the way from the side of the body, up to the nose and head region.
  • In the beginning, the lateral line organ is eroded; later on in the progression of the syndrome, this line will look like it was excavated.

UNCERTAIN CAUSE: Dissections performed on fish showing this syndrome usually yield Spironucleus parasites in the abdominal cavity; some have also found them in the lateral line organ. In my 39 years of research, though, I haven’t found any.

It is still unclear what causes HLLS/HITH, and with the lack of scientific studies, this may not be answered soon. In my opinion, it is a syndrome caused by a mix of problems that occur separately or together: lack of good food, Spironucleus parasites, bad digestion and poor resorption of minerals and vitamins, secondary bacterial infections, unidentified viral infection and other, as of yet unknown, factors.

A good diagnosis remains important to identify certain pathogens. In our experience, treating the Spironucleus infection and adapting the fish’s diet can cure the secondary bacterial infection and the syndrome…since we cured a specific disease! Some fish might have scars left over after being cured.

PREVENTION: This is possible; maintain good aquatic conditions and offer the fish good food with phytobiotics like herbs, such as those found in Biofish Food herbal.


This syndrome occurs in Malawi and Tanganyika cichlids.

SYMPTOMS: (Initial stage)

  • Lethargic
  • Shows rapid breathing
  • Loss of appetite(Advanced stage)
  • Swollen/bloated belly (different than dropsy/ascites with raised scales)
  • Sometimes the anus is protruding.
  • The fish die within a few days.

After examining the fish we usually find excessive fluid in the abdominal cavity and sometimes parasites Spironucleus and/or secondary bacterial infections.

It is yet unclear what is the exact cause of this syndrome. Many speculations have been made but in my opinion, it is a food-related problem.

TREATMENT: In most cases where the fish is not yet showing serious bloating or swollen stomachs, we solved the problem by:

  • Changing the diet to one with more vegetable content, avoiding animal proteins like beef or turkey heart
  • Avoiding mosquito larvae
  • Avoiding produced feed with high fatty content or with too much saturated fatty acids.

We usually recommend extra algae (such as Biofish Food chlorella) or easily digestible vegetable granulated food (such as Biofish Food green) as treatment and prevention.

In some cases, we should not forget that pathogens can be involved: we must treat the parasites Spironucleus and secondary bacterial infections.


This syndrome with a high mortality rate is well known among discus, angel fish, and uaru. The first reports of this problem reached us in 1986.

SYMPTOMS: Fish thus afflicted have:

  • An excess of mucus on the skin and in the gills
  • Respiratory difficulties
  • Darkened coloration.

Microscopic investigation sometimes reveals bacterial and/or parasitic infections and in some cases, these infections, like bacterial infections, are secondary.

Sometimes, this syndrome appears when low atmospheric pressure occurs in combination with high humidity, especially for newly imported fish.

COMPLICATION: In some cases, by placing a discus or angel fish from different places of origin in the same row (fish house), or mixing them together in an aquarium makes them sick, especially if one is from Asia and the other is from Europe; for some reason, combining the two places of origin raises the risk for this pest. Fish originating from the same town or province have less or no risk.

This syndrome has not yet been scientifically studied. The symptoms look like an allergic reaction, what with the ‘slimy’ reaction of the skin and gills that produce excessive mucus. Many of the discus or angel fish are raised in specific, enclosed systems without any contact with other ‘foreign’ discus or angel fish.

It seems that these fish have no resistance or no immunity against a contaminant from the other fish. But after several days (usually weeks), the fish that survive show good health and will have developed a resistance to whatever it is that makes them sick. Some blame this on a virus or bacteria, yet no real conclusions can be drawn since each case seems to be different. We have still much to learn about this syndrome.


  1. Make the correct diagnosis: use a microscope and you may find the causative pathogen.
  2. Use fish food with immune-stimulants to strengthen the resistance of your fish.
  3. When the symptoms start to exhibit themselves, do lots of water changes (every 24-48 hours) and, when necessary, add medicine against secondary infections.
  4. Fish need time to recover; have patience because this can take several weeks.

PREVENTION: We recommend not mixing species from different places of origin; try to always buy your fish from the same source.

Dr. Gerard Bassleer has 39 years of experience as a fish pathobiologist in the industry of ornamental fish, and his discussion of these diseases are based on his encounters with them in the course of his practice. Cichlids are still popular with hobbyists; Dr. Bassleer’s last estimate is that they represent between 15 to 20% of the aquarium hobby, particularly the discus, Malawi, and Tanganyika cichlids. His objective for this article was to discuss recent findings on diseases and syndromes for African and American cichlids. Not covered here is the small group of Asian cichlids such as the etroplus. For a more extensive discussion, interested readers may pick up a copy of his book, “The New Illustrated Guide to Fish Diseases,” which comes with a thousand photographs.


This appeared in Animal Scene’s February 2017 issue.