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Fish Cillin (Ampicillin) 250 mg, 100 Capsules
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Thomas Labs Item #: 1013950 -

Fish Cillin (Ampicillin) 250 mg, 30 Capsules
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Thomas Labs Item #: 1013951 -

Ampicillin Fish Antibiotics

Fish Cillin is a pet medication for ornamental and aquarium fish. Fish Cillin contains ampicillin which is effective against gram-positive and some gram-negative bacteria which cause bacterial fish diseases like aeromonas and gill diseases.

Fish Cillin is a broad-spectrum antibiotic for fish that treats and prevents numerous common bacterial infections, including flexibacter infections and fin and tail rot. A single capsule treats an entire tank of fish, with most symptoms improving within days of beginning therapy.

Benefits of Fish Cillin:

  • Broad-spectrum activity
  • Improves activity and energy levels in fish
  • Can be used in cats and dogs
  • Conveniently available over the counter
  • Effective against gram-positive and certain gram-negative bacteria
  • Treats skin, respiratory, and urinary tract infections in dogs, cats, and small animals
  • Treat entire tank at once instead of treating individual fish
  • Usually well tolerated

Use only as directed by your veterinarian. Do not give this medication to fish or other animals with an allergy to it or to penicillin. Do not allow children to administer this medication.


  1. Add one 250 mg capsule into your aquarium for every 10 gallons of water.
  2. Perform a partial water change between 18 and 24 hours after dosing your tank.
  3. Add another 250 mg capsule per 10 gallons of water to your tank 24 hours after the first dose was administered. Continue dosing your aquarium once daily for 5 to 10 days.
  4. Stop treatment if no improvement in your fish is noted after 5 days.
  5. Treat dogs and cats with 9 to 18 mg per pound of body weight every 8 hours.

Frequency of Use:

Give Fish Cillin for at least 5 days and for no longer than 10 days unless specifically told otherwise by your veterinarian.


Store Fish Cillin at room temperature, out of reach of pets and children. Keep in the original packaging.

It is a violation of Federal Law to use this product in a manner inconsistent with its labeling.

The active ingredient in Fish Cillin, ampicillin, works by preventing bacteria from properly forming cell walls. Without a cell wall, unwanted substances are allowed to enter the cells and the cell contents are able to leak out. This action kills the bacteria responsible for infection.


Keep this product out of reach of children and animals. Do not use or store in or near open flame or heat.

Fish Cillin is intended for use in aquarium and ornamental fish only. It may also be given to dogs and cats with veterinarian approval. Not for use in horses or human.

CAUTION: This medication may cause severe diarrhea when given orally at high doses.

Do not give Fish Cillin to animals allergic to penicillin.

Short-term use of this medication does not usually cause side effects. If your pet experiences an adverse reaction to Fish Cillin, consult your veterinarian for advice.

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