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Tetracycline: use and recommendations

Other names: There are four naturally occurring tetracyclines and half a dozen semi-synthetic versions, as shown below.

Naturally – chlortetracycline, demeclocyline, oxytetracyline, tetracycline

Semi synthetic – doxycycline, limicyline, meclocycline, metacycline, minocycline, rolitetracycline

Action: Broad spectrum antibiotic.

A healthy aquarium

History Uses

Chlortetracycline was the first member of the tetracycline group, and was derived from a soil bacterium discovered in the late 1940s. In 2005, a new subgroup of tetracyclines called glycylcyclines. These new antimicrobials are used to treat drug-resistant infections that do not respond to standard tetracyclines.

In ornamental fish, tetracycline is used to treat a variety of external and internal bacterial infections, including these disorders:

  • Hemorrhagic septicemia – Bacterial infection of the bloodstream. Characterized by bloody streaks on the body and fins.
  • Cotton Mouth Disease – Bacterial infection that affects the mouth with fungal, like growth and erosion of the mouth parts.
  • Fin breakage – Fins and tail become torn and frayed, in some cases almost completely eroded.
  • Gill disease – Fish breathe heavily and the gills appear bright red.
  • Open Body Sores – Bacterial infection that causes open red sores on the body.
  • Body Slime – Slimy spots appear on the body, the fish flash against objects and breathe rapidly.
  • Pop-eye – The eyes are cloudy and may protrude from the head.
  • Cyanobacteria – It is also used to treat cyanobacteria (blue-green algae).

In general, tetracycline is more effective against aerobic bacteria, especially gram-positive organisms. In infections caused by gram-negative bacteria, minocycline is more effective than tetracycline. Tetracycline becomes more potent as you age, so expiration dates must be carefully followed.

Tetracycline will kill nitrifying bacteria, so avoid using it in conjunction with other antibiotics to reduce the impact these drugs have on biologics. Monitor water chemistry closely for several weeks after treatment with this antibiotic, testing for ammonia and nitrite. Avoid the use of this drug if the fish are already suffering from ammonia or nitrite poisoning, or diseases that have already caused the fish to become significantly anemic.

High general hardness (GH) will reduce the effectiveness of this drug. Tetracycline is not effective at all when the pH of the water is above 7.5. Remove any carbon filter media when using this medication, as it will remove tetracycline from the water. Tetracyclines can be safely used in conjunction with methylene blue.