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Pond Fish Diseases: Parasitic Infections

Hi, Melissa here. As the pond season is coming to a close I figured I would write one more article about pond fish diseases so when next spring arrives you will be ready to treat any creepy crawly things scampering over your fish.

Along with bacterial infections, koi and goldfish are also very susceptible to parasitic infections. Parasites are crawling around everywhere, but the majority are microscopic and never seen with the naked eye. There are a few parasites that are visible with the naked eye. Fish lice, anchor worms, leaches, and ich are among the few parasites that can be seen without a microscope. Most parasites themselves are not particularly deadly, but they will set the stage for further infections that will ultimately lead to death if left untreated. Parasites irritate fish by latching on to their gills, scales, or other soft tissue to feed causing a lot of stress. Once a fish is stressed, they become very susceptible to infections. Bacterial infections are very common in conjunction with parasitic infections. Some symptoms of parasites include flashing, white spots, clamped fins, respiratory distress, erratic swimming, white and slimy feces, red sores, among others. If any external parasites are observed medications with the active ingredient diflubenxuron, praziquantel, and trichlorfon are a good choice. Some medications that we sell containing these ingredients include, anchors away, dimlin, parasite guard, and prazipro.

Parasitic infections are not directly caused by poor water quality, unlike bacterial infections, thus prevention is a little harder. Quarantining new fish and plants are highly recommended. Fish should be housed in a hospital tank for several weeks for observation and plants should be dipped before added directly to a pond since plants can carry unwanted parasite eggs. Some people suggest a very dilute bleach solution to dip the plants in for a few seconds then rinse in dechlorinated water. Others suggest potassium permanganate (use just enough to turn the water pink). Plants could also be placed in a quarantine tank for a few weeks as long as the plant are receiving the correct lighting.

So the take home lesson here is…”Learn from the mistakes of others, you won’t live long enough to make them all yourself!” ..ALWAYS quarantine new arrivals. Nobody wants to have thousands of dollars turn belly up because of one careless mistake.



  1. avatar

    Have a question regarding my goldfish (Comet and Shubumkins). One of my fish (comet) is twice the size it should be. Looks pregnant. Was like that all last summer and I thought it would not make it tru the winter but has. Looks like a tumor or very pregnant. Do you know what it is? The other 45+ fish look fine.

  2. avatar

    Comets carrying eggs will have an enlarged abdomen. Are the scales still flat, or are they standing up making the fish look like a pone cone? If they are standing, the fish has dropsy, amd it would be bestto remove it from the pond to either attempt treatment or euthanize humanely. If the fish is carrying eggs, you may see males in the pond chasing the fish to spawn. You may want to put some bunches pf anacharis or hornwort in the pond for the fish to lay eggs in so they can release them. It could also be a tumor or some other disorder, but if the fish is eating and swimming as usual, good possibility she is carrying eggs. If possible, snap a photo and send it to marinebio@thatpetplace.com, and we can have a look to try and confirm. This link: http://www.wetwebmedia.com/fwsubwebindex/gldfshreprofaqs.htm may also be helpful.

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