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Fish Zole (Metronidazole)

By | Last Updated: 23rd February 2023

What is Fish Zole

Fish Zole is the brand name for the antibiotic metronidazole meant for ornamental and aquarium fish. This medication is given to treat bacterial infections from Chondrococcus, Pseudomonas, and Areomonas genera, as well as parasitic infections like gill diseases, hole in the head, and angel problems (in discus and cichlid). Fish Zole is not used in fish intended for human consumption [3, 4].

Quick Information

Fish Zole

Generic Name (Active Ingredient): Metronidazole

Brand Name: Fish Zole, Fish Zole Forte

Manufacturer: Thomas Labs

Type: Antibiotic

Who can take it: Fish

FDA Approved: No [5]

Availability: Over-the-counter

Available forms: 250 mg and 500 mg Tablets

How does Fish Zole work

It has a strong bactericidal action on most gram-positive, and a few gram-negative bacteria, being particularly effective against anaerobic (i.e. growing without oxygen) bacteria [4].

Dosage and application

Being an over-the-counter medication, you can follow the instructions provided on the label regarding how to use it, but it is suggested to talk to a qualified vet first. The dosage usually prescribed is one 250 mg tablet per 10-gallon water, to be repeated every 24 hours, with partial water changes suggested between treatments.

The usual duration of the treatment is 5-10 days. If after stopping the treatment, the condition recurs, get in touch with the vet, which you may also need to do if there is no improvement after the first 5 days [2, 4].

At the end of the treatment, the water in the aquarium may turn yellow. Although harmless, you can correct this by changing about 20% of the water and using a charcoal filter [4].

Safety and side effects

There are no known side effects, but make sure to call an expert immediately if you ever overdose your fishes.

Should Fish Zole be used for anyone other than fish

Pet owners may consider giving Fish Zole to their dogs or cats for bacterial conditions because it is available without a prescription, in addition to being relatively cheaper than other formulations for the generic metronidazole. However, it is not safe to do so.

Some people might even take it themselves to treat conditions like endocarditis, giardiasis, and pelvic inflammatory disease. But this practice should also be avoided to stay away from serious adverse health effects.


    1. Fish Zole (Metronidazole) – EntirelyPets.com
    2. Fish Zole – walmartpetrx.com
    3. Thomas Labs Fish Zole (Metronidazole) – PetMountain.com
    4. Fish Zole – Metronidazole – fishmoxfishflex.com
    5. FISH ZOLE- metronidazole tablet –  DailyMed.nlm.nih.gov
    6. Fish Zole (Metronidazole) – Allivet.com

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