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You are here: myPetSmart.com > Care Guides > Informational Guide Fish Treatment

Informational Guide (Fish Treatment Guide)

Fish Treatment

Did you know? There are a variety of organisms that can cause problems for aquarium fish, however in many cases poor water quality largely impacts fish loss. Check the water quality whenever fish are sick. Always read carefully and follow directions on medication labels. Know the correct water volume of your aquarium to ensure proper dosing of medication.

Disease Prevention

Fish may be carriers of parasites or bacteria without showing signs of disease. When fish are stressed, due to factors such as poor water quality, handling and transportation, or injury, diseases are more likely to occur. Maintaining proper water quality and good nutrition will reduce stress and help prevent diseases from occurring.

When adding new fish to an aquarium, it is important to monitor the fish for illness. Ideally, new fish should be quarantined in a separate isolation aquarium for a few weeks before adding them to your aquarium. Fish in the isolation tank can be medicated, if necessary, without affecting the main aquarium.

Always wash your hands before and after handling fish or cleaning your aquarium. Keep all medications stored safely, out of
reach of children.

Causative Organism Disease Signs
Treatment and Ingredients
Lymphocystis White irregular growths extending
from fins or skin
Cyprinid Herpesvirus-1
(Carp Pox)
Raised smooth bumps on fins or skin
of Koi
(Water mold)
Long whitish cotton-like filaments
on fins or skin, also can occur on fish
eggs, uneaten food, or on dead fish
Malachite Green
Methylene Blue
Fin and tail rot, skin ulcers, dropsy
(ascites), pop-eye, red fins and skin
(same signs can also be caused by
Gas Bubble Disease)
Minocycline Antibiotic
Erythromycin Antibiotic
Melaleuca Extract
(Flexibacter) columnaris
Fuzzy skin or lip lesions
NOTE: Bacterial infections often occur with
poor water quality or when fish have
parasite problems
Ensure proper water quality and treat for parasitic diseases.
Skin Parasites:    
multifiliis (Ich)
White spots on body and fins,
scraping body on rocks (flashing)
Formalin/Malachite Green
Increased slime coat (white or
grayish cast on skin).
Increased gill movement, fins
clamped to sides, lying on bottom
(Velvet Disease)
Golden speckled cast on skin Copper sulfate
Internal Protozoa Parasites:    
Spironucleus (Hexamita) Lesions in Cichlids along head and
lateral line (Hole-in-Head)
Red worms protrude from vent;
Poor growth, weight loss
Skin and gill flukes,
Encysted Digenean
Inflamed gills, excess mucus on skin,
scraping body on rocks (flashing)
Leeches and other
Worms on outside of fish or in tank
Fish Lice (Argulus) Small discs that move across the
skin of the fish, or swim through
the water

Anchor Worms


Gray to white worm-like parasites
attached to the fish’s skin; the head
is embedded under the skin

Follow label dosage instructions for using each product.

Water Quality Testing
PetSmart offers free aquarium water testing. By bringing in a sample of your aquarium water, we can test the quality within minutes. See the Setting Up an Aquarium Guide for more information about water quality and water testing.


Things to Watch For
• Unusual swimming pattern

• Thinness or decreased appetite

• Abdominal swelling

• Inflamed or discolored skin or fins

• Fins clamped to sides of body

• Scraping body on rocks (flashing)

If you notice any of the signs described above, speak with a PetSmart store associate or a veterinarian about the health of your pet.