The smallest Parasite of the greatest importance to goldfish, Koi, tropical fish, Siamese, fighting fish, or bettas, would have to be Hexamita.

It’s a little parasite you may have heard about, because it causes something called “hole in the head disease” but actually, if it gets your fish, you would actually see weakness, peeling skin, erosion of the fins, and weight loss. Crazy weight loss.

But remember: Peeling skin, weightloss.

Peeling cracking skin, weightloss. Peeling cracking skin, weightloss. Peeling cracking skin, weightloss. Peeling cracking skin, weightloss. Peeling cracking skin, weightloss. Peeling cracking skin, weightloss. Peeling cracking skin, weightloss. Peeling cracking skin, weightloss. 

Ph crash and/or Ich do NOT cause peeling/cracking of the skin nor weight loss.

They ALL, do cause weakness, clamped fins and mucus slime @ skin!

There really isn’t a species of fish that is immune to hexamita. However, I see it kind of a lot more in Goldfish, angelfish, discus, Oscars, among others.

Fortunately, it’s really easy to treat. In fact I am managing several cases right now. At the same time, I am gathering information regarding how fast Hexamita clears with the treatment, but also what the impacts on biological filtration are when you treat the tank directly.

As a parasite, Hexamita is difficult to diagnose. It’s quite small. It is 1/10 of the size of Costia. And Costia is pretty small. Typically, Costia is 1/50th of the size of ick..

What this means:

On the average microscope which a hobbyist would have, you are probably going to need the highest power that the scope is capable of. Most microscopes have a 4x, a 10x, and a 40x optic. The ocular is often a  10x ocular.

It is probable that you are going to need 400x – which is the 10x ocular and the 40x optic.

Sometimes, at 100 times magnification, you can get an idea for the swarming organisms if you look closely but to confirm, you will need to use the highest power the average scope is capable of.

What you see under the microscope is a swarm of microorganisms. They are flagellate protozoans. Means, they have a tail.

I think the reason I’m seeing more and more Hexamita is because I’m seeing less and less of the other parasites. And I think that’s because the pet stores and the individual hobbyists are all better and faster at treating the parasites. There are some really good medicines out now. People are quicker to use salt so I believe that with a decline in the commonality of the regular ciliates is creating the illusion that Hexamita is on the rise.

When I see Hexamita, it’s my clinical opinion that you can’t delay the application of Metronidazole. What I have found is that you can at least STOP the progression of the disease with the first application and with luck — you may find even the worst of the cases reversible. Or not.

So there are two things about Hexamita before we get into treatment.

First, Hexamita has a direct life cycle. This means that Hexamita may be in the millions on the fish and in the environment. (Yes it’s environmental) and it reproduces by binary fission into trophozoites. So one organism becomes MANY with each division. And these trophozoites are immediately and directly able to infect the host. So the affected fish is quickly ‘swarmed’ and overrun with Hexamita organisms. The organisms attack all epithelium/epidermis including the gills. And that’s where the fish takes the hardest pounding.

MANY people would say: “Wait, what? I think of Hexamita as a gut infection.”

For many tropical fish hobbyists and breeders, it is. A gastrointestinal infection with Hexamita is a good place to hide Hexamita that can then infect the surfaces of the host and of other fish. Weight loss is the most common sign of intestinal Hexamita and it’s pretty easy to diagnose in fecal samples, direct dark field or light field whichever you’re better at.

The infections that are MOST deadly are the skin and gill cases. The idea is that with the death of so much superficial epidermis, the fish lose plasma and take on water. “Dropsy” can results. Fortunately, this is one form of Dropsy that is “treatable” if you can just close the skin as an avenue of ingress of water, and egress of plasma proteins.

Salt is helpful, certainly. Some people hold out that 0.3% salt, even 0.6% salt are effective. Whether they actually checked for surviving Hexamita organisms, I do not know. Perhaps it just closes the gap between the osmotic “inside and outside” of the fish and reduces water intake. Perhaps it just increases mucus production on the skin, and also reduces the water balance issue.

This article (HERE) has a little more depth on the lesions created in fish. From “Hole in the Head” in Oscars to wasting in Discus and even the skin and fin lesions you see in Goldfish. Also described are the “melanophore migration” or blackening of the skin after a Hexamita infection is cleared.

The second thing I need you to be aware of is the influence of nutrition and water quality in the sufferers / hosts.

Hexamita is almost-never a successful pathogen in super-clean ponds, tanks. I believe this is why it’s more common in Oscar tanks and Goldfish tanks because these type fish are HEAVILY fed for best results. And then the organics in the system are high and that is PERFECT for Hexamita Spironucleus.

Frequent or even continuous water changes (Trickle Systems) are practically immune to Hexamita.

Fish that are fed complete and balanced nutrition are also “less likely” to suffer with Hexamita Spironucleus.

Let’s Recap

1. Hexamita is common in tropical and nontropical fish especially Oscars Discus and Goldfish
2. Hexamita is an infection that you most often see in dirty tanks
3. Hexamita causes lethargy, weakness, weight loss and cracking peeling skin and mucus
4. Hexamita can be reversed if treated quickly

Treatment of Hexamita

Perform a water change of up to 60% and replace the water with dechlorinated water that’s close in temperature AND close in pH  –  if you use SeaChem Neutral Regulator it’s less of a worry because the main system will have a neutral pH and the replacement water will be neutral AND dechlorinated by using SeaChem Neutral Regulator.

After the water change, calculate the tank volume. That’s length x width x depth in inches, divided by 231.

So a tank that’s 24″ by 24″ by 32″ would have the volume of about 80 gallons. ( 24″ x 24″ x 32″ / 231 = 80 gallons )

The dose on Metronidazole is 500mg per 10 gallons of water (when applied to the water.)

The impact on gram-negative Anaerobes is severe. But the impact on ‘nitrifying aerobic bacteria’ is much less. It could be said that Metronidazole DOES NOT IMPACT BIOLOGICAL FILTRATION and I believe that “to an extent” however I do (always) see clouding in the tank after treatment. SO I am very sure it upsets SOME part of the equilibrium. However, sponge filtration and Tetra’s Pond Clarifier (even in tanks) clarifies this VERY well.

For our 80 gallon aquarium, we need 8 tablets of 500mg Metronidazole (or the label dose of Metroplex which is over the counter Metronidazole.)

HOW TO USE THE METRONIDAZOLE

Put the Metronidazole tabets in fresh water in a Nutribullet or similar and blend it quite thoroughly. The contents of the blender will turn into a white “emulsion”. Be sure that the tablets are COMPLETELY dissolved / distributed and broken up in the process.

Pour that white Metronidazole emulsion in the tank in several places. If you pour it directly on a fish, it’s okay. They will choke and cough except that’s unnecessary and harmless.

My favorite distribution point if the outlet of a filter or pump. This has the best distribution in the water column.

I recommend two doses back to back. Day one, and Day two.

Then do two or even three more dosing, every 48 to 72 hours.

In the olden days we might have dosed ONLY TWO TIMES and we saw good results in Goldfish. But I don’t know if “we got it all” doing it that way.

• Day 1: Metronidazole from aggressive blender as emulsion 500mg per ten gallons.
• Day 2: 500mg/10gal Metro emulsified
• Day 4: 500mg/10gal Metro emulsified
• Day 6 or Day 7: 500mg/10gal Metro emulsified

Metronidazole can be used in the food and this is especially good for gut forms of infection. Getting metronidazole in a medicated food or top-dress is entirely possible, but I am not crazy about the amount of work in that compared to several doses of metronidazole in the water.

If the water gets cloudy as above, PLEASE clear the clouding with a sponge filter and some water clarifier as described above.

Toxicity of metronidazole to the common pond and tropical fish is LOW. Treating fish in the main system should be accompanied by:

1. Turning off the UV if present
2. Remove Carbon from the system
3. Remove (or expect to lose) all your invertebrates. Crayfish and clams will die.