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10.2.1. All Protozoans

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Author : David Bogert

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4 minutes
Difficulty : Level 7

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What are the skin diseases found on aquarium fish?
10.2.1. All Protozoans on Aquarium Fish
10.2.1. All Protozoans on Aquarium Fish

Many aquarium diseases are caused by external protozoan (single celled) parasites. External protozoan parasites of freshwater fish include ich, velvet, chilodonella, costia and epistylis. Most of these organisms follow a very similar course with the fish.

They first infect the gills of the fish in large numbers. This is where a fish breathes. So, the fish gets what in persons would be emphysema or COPD, the fish gets “short of breath”. The fish blood oxygen goes low, and the fish hangs close to the surface where the water’s oxygen level is the greatest. The fish moves its gills rapidly, looking like it is panting. The fish gets lethargic and doesn’t want to eat. The fish may hide or clamp its gill and fins. Sometimes the fish hangs on the bottom of the aquarium.

This is a point where many experts disagree on what to do. The “return to loincloth” folks treat with garlic, many experienced aquarium owners will just wait and see what happens, some will transfer to hospital aquariums and treat the fish, and some will treat the whole aquarium.

Chilodonella on an aquarium fish

If no treatment is done, the diseases can go to the next step. The organisms spread from the gills to the skin and become visible to the naked eye. At this point the fish begin “flashing”. Flashing is a fish rubbing its sides in a quick jerky movement on the substrate, plants or décor. “Twitching” and “shimmying” is also seen. Look for the organisms on the fish. Sometimes there are just patches of white or excess skin mucus.

Treating most skin protozoan diseases can be done with a whole series of steps:

  1. Add lots of additional biofiltration (under-gravel, canister or sump) to filter out and thus kill the free swimming organisms. This added biofiltration also reduces the bacterial loading in the water which in turn allows the fish to devote more immune system resources to the pathogen.
  2. Add a formalin/malachite green medication (Ich-X, Rid-Ich Plus, Blue Planet White Spot Remedy and Mardel QuickCure) or a Copper based medication (Cupramine, Copper Power, Copper Aide or Copper Safe) to the water of the aquarium to kill the free swimming organisms.
  3. Do not put the fish in a hospital/quarantine tank
  4. Do not change out or clean the filter media.
  5. Do not raise the temperature of the tank
  6. Add a 24/7 UV sterilizer to kill the free swimming organisms and reduce the bacterial loading in the water which in turn allows the fish to devote more immune system resources to the pathogen.
  7. Added aeration always is helpful
The Pathogens

White spot or ich (Ichthyophthirius multifiliis) is a relatively large parasite that looks like sprinkles of white table salt on the fish.

Ich on a Goldfish
Ich on a Goldfish

Ich is the most common fish disease, so it warrants several articles in the link below.

10.2.2. Ich

The other external single cell parasites of fish include the following:

  • “Velvet” (Piscinoodinium pillulare, or oodinium, a dinoflagellate algae) is a very small parasite that looks like patches of yellowish to golden fine spots on the fish.

10.2.3. Velvet

  • Epistylis appears as many small white fluffy growths on the external surfaces of fish, including the fins.

10.2.4. Epistylis

  • Chilodonella (a ciliated protozoan) has greyish white patches on the body.
  • Costia (Ichthyobodo, a protozoan) appears as cloudy and milky patches on the fish and is indistinguishable from chilodonella without a microscope.

10.2.5. Chilodonella and Costia

  • Tetrahymena, a protozoan that can imitate ich, chilodonella or costia. In it’s most virulent form it invades the tissues of the skin of the fish and produces large translucent white spots on the body of the fish.

10.2.6. Tetrahymena


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Return to Protozoan Menu


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