Keeping Tropical Fish in an Aquarium: How to Use Salt in Killing Protozoan Parasites

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How to use salt in killing protozoan parasites of aquarium fish plus a video of an amazing fish strategy to get rid of parasites.

Before you read or skip the main contents of this article, please note that an an amazing video can be found at the end of the article. It features a goldfish trying to get rid of its protozoan parasite. At least, this is the author's hypothesis. It must be a rare phenomenon to witness among fishes and is related to its evolution or adaptation to parasitic infections.

Keeping a Freshwater Tropical Fish

Keeping a freshwater tropical fish in an aquarium is a challenging task especially for the neophyte. There are certain things to be observed by the aquarium enthusiast to ensure that freshwater tropical fish like goldfish survive its man-made habitat. Space is constrained in the aquarium and the fishes have no other choice to swim about but its limited environment.

How to Get Rid of Parasites: Which Parasites?

One of the important tasks of the freshwater fish enthusiast is how to keep tropical fish alive in the aquarium. Freshwater fishes are susceptible to parasites unlike the saltwater fishes. In order to get rid of parasites that afflict the tropical fish and threaten its survival, knowledge of the common diseases or parasites of the freshwater fishes is a must. Among those ubiquitous parasites are the protozoans.

Protozoans or one-celled organisms called ich are usually common parasites of freshwater fishes like the goldfish. Below are typical protozooan parasites of freshwater fishes.

Costia picture


Trichodina picture


chilodonella picture


Ichthyophthirius multifilis picture

Ichthyophthirius multifiliis

The word ich or ick derives from the scientific name of the last protozoan parasite named above called Ichthyophthirius. It is a common parasite of freshwater aquarium fish causing white spots. It This condition is called ichthyophthiriasis. It may be causing an itchy sensation to the fish because the fish rubs itself against hard objects inside the aquarium like decorative rocks or pebbles in the aquarium.

Using Salt as a Cure for Ich

Adding salt to the water in freshwater fish aquarium is one of the oldest and easiest cure (as well as prevention) for ich. This is the reason why aquarium sellers usually advice the pet owners to put in some salt into the aquarium before allowing the fish to settle there. The purpose of the salt is to get rid of parasites or their reproductive cysts that may have incorporated themselves in the materials (like pebbles and sand) placed into the aquarium. These cysts hatch when water is introduced into it. An ideal solution of 0.3 percent salt is usually adviced but would vary depending on fish species.

In one of the forums in, it was adviced that salt can only be used to control ich infections in small volumes of water like in the aquarium but not of course practical in large volumes of water like those found in ponds. Alternatively, fish can be dipped in a 3% salt solution for thirty seconds to several minutes. Lower concentrations of salt will require a prolonged bath. To speed up the effect of removing the protozoan parasites, the temperature of the aquarium may be increased so that the life stages of the parasite will be hastened and made susceptible to the greater concentration of salt thereby killing it. 

Freshwater fish like the gold fish may be able to tolerate greater concentrations of salt if done gradually. It is suggested that about one teaspoon per gallon of water must be added every three 12-hour intervals then let the salt concentration stay as a form of therapeutic treatment for the fish for seven days. This should get rid of the protozoan parasites. After the seven day treatment, one-fourth of the water in the aquarium must be removed everyday for a consecutive number of days to bring back the water in the aquarium to lesser concentrations of salt. Thus, the aquarium fish will be acclimatized to the new environment gradually.

A New Kind of Parasite?

This author encountered a protozoan parasite afflicting their pet goldfish. This is unlike all the parasites mentioned above. He took a picture of the parasite clinging unto the goldfish. Here it is:

goldfish parasite picture

The parasite clinging on the side (just back of pectoral fin) of the goldfish (Image Source)

The parasite clung there for a few days. Several days later, two of the four goldfish died after sustaining black marks on their body scales. The author tried to get a closer look of the parasite by magnifying a protozoan parasite that bogs the fishes. Here's how it looks:

goldfish parasite image

The protozoan parasite (Image Source)

The protozoan parasite is unlike any protozoan mentioned and shown in the pictures above that afflict freshwater fishes. He looked for a similar image in Google but his search was in vain. Maybe somebody can extend help on this.Only one of the four goldfishes survived and is still under salt treatment at this time.

The author noticed something unusual with the behavior of the remaining goldfish. It keeps on ingesting some pebbles and spit it out with such force. Maybe it is trying to get rid of the parasite inside its throat or gills, or maybe the stomach. See the short video below on how the goldfish does this. It's amazing. Maybe it is some kind of adaptation or strategy of the remaining goldfish to survive. In fact, among the four goldfish, it is the only one that survived the parasites.

Lithophagy in goldfish.


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