Metronidazole, Metro
Ardan Huck May 31, 2002

I just wanted to help people understand the drug Metro and its primary use for dealing with fish.

Metro is mainly used as an anti-flagellate in fish intestines and organs. It kills flagellates. Flagellates are single celled protozoa (most are oval shaped). They move by a small "whip like" organ called a "flagella" (some have one flagella, some have multiple flagella). In treating fish, Metro is mainly effective against "Hexamita, Spironucleus spp., Trichomonas spp., and Protoopalina spp." (all intestinal flagellates) (protoopalina is often confused with a ciliate, it is not proven to be a real parasite to fish) (Untergasser).

Metro does not affect worms. It does have some effect on Ich, and on Cryptocaryon (marine ich). Metro does have a "very limited" antibiotic effect (kill bacteria). Mainly bacteria named Campylobacter fetus bacteria, and Corynebacterium vaginalis (Untergasser).

It has some limited effect on some other bacteria depending on concentration. It is less active against non spore forming, gram positive bacilli and even less active against gram positive cocci (Untergasser, Handbook of Fish Diseases).

Now, there are some flagellated bacteria ("Microbiology in Patient Care" by Morello, Mizer, Wilson). Effectiveness of Metro is limited to very specific bacteria. Metro kills the organisms by "disrupting the DNA of the organism after it enters the cell" ("The Pill Book" by Bantam Books, Silverman,Simon).

My point: Metro is mainly used as an antiflagellate in fish intestines, not as an antibiotic when using for fish.

Extra info: There are flagellates of the fishes' blood, skin, gills, and other organs. However, Metro is not listed as effective against these flagellates according to Untergasser.

Here are some links with additional info on this drug:

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