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One of the problems that many fish keepers face is the daunting task of identifying problems in the aquarium.
Unfortunately, lack of experience, or subtle signs of stress can let a disease run rampant until it destroys the
infected fish (sometimes the whole aquarium). I have included this page simply as a guide for diagnosing diseases
in Tropical Fish. It is by no means complete, and I cannot guarantee that it is 100% accurate, but should help
steer you in the right direction.

Always ask your local merchant if the medication you are buying is right for the disease you are trying to cure.




Fish may dart and gasp.

Acidic Water

Acid from fish wastes or decayed food. Acidic
water can iritate gills and skin.

White water line. Plants die, fish have frayed
fins. Alkaline water can destroy gill and fin tissues. Ammonia
becomes more toxic.

Alkaline Water

Seashells or limestone in tank or hard water

Fish die. Water may be cloudy.

Ammonia in Water

Product of decaying wastes.

Threadlike worm hanging from fish. Base of
anchor worm may be red.

Anchor Worm

A parasitic crustacean (Lernaea).

Quarter inch bubble like lumps slowly moving
on skin and fins.


A parasitic crustacean. Sometimes Ergasilus

Fish floats with fins closed.

Betta Pinch Fin

Gill parasites.

Small black specks on skin.

Black Spot

Small fish worms (Diplostomulum).

Red streaks on fins, especially goldfish.
or Bacterial Infection

Gyrodactylus parasites (monogenetic trematodes*),
possibly bacterial septicemia

Fish dying within 24 hours. Gills become

Chloramine in Water

Water company adding chloramine as a
substitute for chlorine.

Fish dart about. gills pump furiously.

Chlorine in water supply

Chlorine added to water supply to kill

Fins held close to body, especially in
livebearing fish.

Clamped Fins

Gill or body parasites.

Water not crystal clear in established tank.

Cloudy Water

Wastes, small animal and plant life. Possibly
over feeding.

Small particles suspended in water causing a
cloudy look.

Cloudy Water in New Tank

Floating silts from gravel especially newly
set up tanks.

White cotton sprouting from fins or body.
possibly Bacteria

A bacteria, Flexobacter (Chondrococcus)
or Fungus

Fish act very

Contaminated Tank water

Chlorine, chloramine, copper or manufacturing
oils in the water.

Grey film on all or part of body.

External protozoan parasite (costia necatrix).

Gills hang partly open at all times

External Parasites (Dactylogyrus)

Small gill parasites (monogenetic trematodes).

Fish darts about wildly and may smash into

Discus Head Worms

Parasitic protozoa in sinus canals of head.

Fish bloated with scales standing out. Fish
resembles a pine cone.


Kidney or Liver Damage
(possibly both)

White film on eyes.

Eye Cloud

Eye injury. From handling or breeder fighting,
possibly bacterial Infection

Fins ragged with jelly at edge of ragged

Fin Fungus

This is not a
disease exactly, but can be cured by improving water quality

Fins eaten away with redness at base of bad

Fin Rot

Sprolegnia fungus with Pseudomonas or
Aeromonas bacteria.

Fish swim aimlessly. May have spasms.
Bacterial Infection
Internal Flavo Bacteria

Small lumps under skin or on fins.

Flesh Worms

Parasitic worms.

A light grey cottony growth or patch on any
part of the fish.

Fungus (grey)

A parasitic fungus, Saprolegnia.

A white cottony growth or patch on any part of
the fish.

Fungus (white)

A bacteria, Flexobacter (Chondrococcus)

Open sores on Gouramis or other anabantids.

Bacterial Infection (Furunculosis)

Aeromonas salmonicida bacteria.

Gills hang partly open and may pump fast.
Gills may pump fast. Gills may appear red.

Gill Flukes

Small gill parasites (Gyrodactylus)
monogenetic trematodes.

Fish rocks back and forth while staying in

<a name="RANGE!B29">Gourami Disease</a>

Dactylogyrus parasites (monogenetic trematodes*).

Skin looks grey in patches.

Costia necatrix parasites.

Fish scrape on objects in tank.

Gyrodactylus parasites (monogenetic trematodes*).

Red steaks on fins usually near body with no
sign of skin damage.

Hemorrhagic Septicemia

A bacteria, Aeromonas (liquefaciens)

Tiny tree-like animals attatched to objects in


Carivorous microanimal

White sugar-like
crystals on fins or body of fish, fish scrape against objects in

External Parasite (ICK
aka ICH, possibly others))

Ichthyophthirius multifiliis, a parasitic

Fish are thin and act listless

Internal Parasites or
Internal Bacterial Infection

Tiny internal parasites
or Bacterial Infection (wasting diesease)

Fish may go to top or bottom or dash about
when first introduced to the tank.
Tank water is
vastly different from original source water

Change in water from which fish are first

Stains on glass or ornaments.

Iron In Water Supply

Dissolved iron in water supply.

Insoluble white deposit or water line.

Lime Deposits on Glass

Caused by lime, a mineral found in water
supplies or from salt buildup.

Fish stay in one place buy wiggle, wag, or

Livebearer Disease or Molly Disease

Water lacks electrolytes needed for normal

White cotton sprouting from mouth sides.

Mouth Fungus

A bacteria, Flexobacter (Chondrococcus).

Flesh eaten away around mouth.

Mouth Rot

Saprolegnia fungus with Pseudomonas or
Aeromonas bacteria.

Color fades from red line. Line may turn

Neon and Cardinal Disease

A parasitic protozoan, Plistophora

Fish dart about. Gills pump furiously
after a water change.

Dissolved gasses or metals in the water.

Dissolved gasses or metals in the water.

Body skin of fish appears dusty in yellowish
or grey patches.

Oodinium (also called VELVET or RUST)

A parasitic algae, Oodinium limneticum.

New Fish act stunned or gasp at top of water
after releasing them from bag.

Oxygen Deprivation, CO2 Poisoning, Ammonia

Ammonia and carbon dioxide suffocating fish in

White water lines. Plants die, fish have
frayed fins.

pH Bounces Back Up after Being Lowered

Hard water supply. Seashells or limestone in

Eyes stand out from sockets.

Pop Eye

Infection from fighting, possibly a bacterial
infection causing fluid to accumulate behind the eyes

Flesh decays at the mouth or tail.

Rot, Fungus

Saprolegnia fungus with Pseudomonas or
Aeromonas bacteria.

Frayed looking fins and moldy looking slime on

Saprolegnia Fungus

A true fungus called Saprolegnia invades the
gills causing suffocation.

Small fish, especially neons, angels and
guppies die without visible symptoms.

Saprolegnia Fungus

A true fungus called Saprolegnia invades the
gills causing suffocation.

Fish swimming with head down (not level).

Swim Bladder Disease

Bladder infection.

Fish thin and weak.
Parasites or

internal or external parasites. See
GYRODACTYLUS. Possibly "wasting Disease" a bacterial infection

Water may be cloudy or have an

Too Many Dissolved
organic Compounds

Decaying food or plants.

Article written by Gareth (Aquafiend)

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