Symptoms

Fish Symptom Checker Guides

Start with what you can see: spots, torn fins, swelling, unusual swimming, cloudy eyes, gasping, or appetite changes. These guides explain possible causes, what to check first, and when water or oxygen problems should be treated as more urgent than a photo match.

BreathingSkin and finsBehavior change

Urgent symptoms

Check tank-wide breathing and swelling signs first.

Gasping, rapid breathing, red gills, pineconing, or several fish acting sick at once should trigger water, oxygen, temperature, and recent-change checks.

Community aquarium fish near the front glass, used as breathing context.

Priority guide

Fish Gasping at the Surface? What to Check First

Treat active surface gasping as urgent because oxygen, ammonia, nitrite, heat, or gill damage can worsen quickly. Do not wait for clearer external signs.

Emergency signRead guide ->

Image: Mitternacht90 / Public domain / resized and cropped for layout

Neon tetra in an aquarium, used as breathing and oxygen context.

Priority guide

Rapid Breathing in Fish: Possible Causes and Next Checks

Rapid breathing needs same-day checks. Escalate to urgent action if it becomes surface gasping, affects several fish, or the fish is weak, lying down, or collapsing.

Same-day checkRead guide ->

Image: SOK / CC BY-SA 4.0 / resized and cropped for layout

Corydoras catfish in an aquarium, used as gill-area context.

Priority guide

Red Gills on Fish: Ammonia, Oxygen, or Parasites?

Check the same day. Red gills plus gasping, rapid breathing, or multiple fish affected should be treated as urgent water/oxygen triage.

Same-day checkRead guide ->

Image: Gabriel Resende Veiga / CC BY-SA 4.0 / resized and cropped for layout

Neon tetra with a swollen belly and raised scales.

Priority guide

Swollen Belly in Fish: Possible Causes and Warning Signs

Review the same day if swelling is new, uneven, or paired with appetite loss. Pineconing scales, severe lethargy, red streaks, or breathing trouble are urgent.

Same-day checkRead guide ->

Image: Citron / Public domain / resized and cropped for layout

Betta fish portrait, used as betta body-shape context.

Priority guide

Bloated Betta Fish: Possible Causes and Warning Signs

Review the same day if bloating is new, persistent, or paired with appetite or buoyancy changes. Raised scales, severe lethargy, gasping, or rapid swelling are urgent warning signs.

Same-day checkRead guide ->

Image: NelsonNellie / CC0 / resized and cropped for layout

Symptom finder

Match the visible sign to the first safe checks

Fish is gasping or breathing fast

Ammonia, nitrite, oxygen, temperature, gill irritation

White spots or fuzzy patches

Ich, velvet, fungus, columnaris, bubbles, injury

Swollen belly or pineconing

Feeding, eggs, dropsy-like swelling, internal illness

Torn, ragged, or shrinking fins

Nipping, sharp decor, fin rot, bacterial irritation

Fish is suddenly lethargic

Tank-wide water or oxygen stress, temperature, bullying, visible illness

Gills look unusually red or inflamed

Ammonia, nitrite, oxygen, temperature, gill irritation

When the pattern has a likely name

Compare the symptom with a focused disease guide

Water-quality pattern

Ammonia poisoning

Compare this disease guide when gasping, red gills, or tank-wide lethargy appears, especially after a cycling or filter disruption.

Progressive fin pattern

Fin rot

Compare this disease guide when ragged or discolored fin edges keep shrinking instead of remaining as one stable tear.

Symptom index

Browse fish symptoms by what changed

Breathing and gills

Symptom guide

Fish Gasping at the Surface? What to Check First

Repeated surface gasping with labored breathing calls for urgent checks. Increase aeration, confirm the filter is running, and test ammonia, nitrite, and temperature. Note whether one fish or several are affected; do not wait for a photo result.

Key signs

Mouth opening repeatedly at the surface or filter outflow.
Multiple fish crowding high-flow or high-oxygen areas.

First check: Test ammonia/nitrite and increase aeration immediately.

Emergency checkRead guide

Symptom guide

Red Gills on Fish: Ammonia, Oxygen, or Parasites?

Sudden red or inflamed gills plus fast breathing can point to ammonia, nitrite, low oxygen, heat, or gill irritation. Test the water and check aeration promptly, especially when several fish are affected.

Key signs

Gills look brighter red, inflamed, or irritated.
Rapid breathing, gasping, or staying near water flow.

First check: Test ammonia/nitrite and check aeration.

Same-day concernRead guide

Symptom guide

Rapid Breathing in Fish: Possible Causes and Next Checks

Rapid breathing is often more urgent than external spots because gill or oxygen problems can worsen quickly.

Key signs

Gill covers moving faster than normal for the species.
Fish stays near flow, hides, clamps fins, or stops eating.

First check: Test ammonia/nitrite and check oxygenation.

Same-day concernRead guide

Spots, growths, and skin changes

Close view of white spots on an aquarium fish. — Image: Thomas Kaczmarczyk / Public domain / resized and cropped for layout

Symptom guide

White Spots on Fish: Ich, Fungus, or Something Else?

Start here when you can see white marks but do not yet know the cause. Compare grains, dust, fuzz, flat patches, behavior, breathing, and water tests before opening a disease-specific guide.

Key signs

Distinct salt-like grains on fins, body, or near gills.
Rubbing, flashing, clamped fins, or hiding.

First check: Compare grains, dust, fuzz, and bubbles under angled light.

Same-day concernRead guide

Aquarium fish with visible surface changes, used for growth comparison. — Image: Tze Sin, Tan / CC BY-SA 3.0 / resized and cropped for layout

Symptom guide

Fuzzy White Growth on Fish: Possible Causes and Next Checks

Fuzzy white growth often suggests damaged tissue, but fungus and bacterial problems can look similar. Speed, location, and texture matter.

Key signs

Cottony, fuzzy, thread-like, or cloudy white growth.
Often attached to a wound, fin edge, mouth area, eggs, or irritated skin.

First check: Compare fluffy growth with flat columnaris-like patches.

Same-day concernRead guide

Aquarium fish with a white spot on the forehead, used for rubbing and irritation context. — Image: Helian / Public domain / resized and cropped for layout

Symptom guide

Fish Rubbing on Objects: Possible Causes and What to Check

Rubbing or flashing means the fish feels irritated. Parasites are possible, but ammonia, nitrite, pH swings, and particles can also irritate skin or gills.

Key signs

Quick side-scrapes against gravel, decor, leaves, or equipment.
May appear with clamped fins, spots, dusting, mucus, or rapid breathing.

First check: Rule out water irritation before assuming parasites.

Monitor closelyRead guide

Fins and body damage

Betta fish photographed from above, used as fin-shape context. — Image: Denise Chan / CC BY-SA 2.0 / resized and cropped for layout

Symptom guide

Torn Fins on Fish: Nipping, Injury, or Fin Rot?

Start here for unexplained torn, split, or frayed fins. Clean sudden tears often fit nipping or injury, while shrinking, discolored edges that worsen over time make fin rot a more useful comparison.

Key signs

Clean splits, missing fin pieces, ragged edges, or shrinking fin margins.
Pale, dark, or red fin edges may suggest irritation or infection.

First check: Check nipping, sharp decor, filter intake, and water.

Monitor closelyRead guide

Betta fish with infected wounds, used as red-mark and lesion context. — Image: Ryan O. Hershey / CC BY 4.0 / resized and cropped for layout

Symptom guide

Red Streaks on Fish: Possible Causes and Urgent Checks

Red streaks can be a serious sign when paired with lethargy, ulcers, fin rot, or poor water readings. They need context and water testing.

Key signs

Red lines in fins, body, tail, or near fin bases.
Ulcers, sores, bloody patches, or swollen areas.

First check: Check spread, wounds, behavior, and water readings.

Same-day concernRead guide

Swimming and buoyancy

Goldfish floating sideways with buoyancy trouble. — Image: Humanfeather / Michelle Jo / CC BY 3.0 / resized and cropped for layout

Symptom guide

Fish Floating Sideways: Possible Causes and Next Steps

Floating sideways is a buoyancy sign, not a single diagnosis. It can range from digestive pressure to serious systemic illness.

Key signs

Floating sideways, upside down, nose-up, tail-up, or sinking.
Trouble holding position or reaching food.

First check: Check swelling, feeding history, posture, and water.

Same-day concernRead guide

Swelling and bloating

Symptom guide

Swollen Belly in Fish: Possible Causes and Warning Signs

Belly swelling can be mild or serious. Pineconing scales, lethargy, and appetite loss are important warning signs.

Key signs

Round belly, uneven swelling, or full-body bloating.
Raised scales from above, appetite loss, hiding, or lethargy.

First check: Use a top-down view to check for pineconing.

Same-day concernRead guide

Symptom guide

Bloated Betta Fish: Possible Causes and Warning Signs

Betta bloating is common but can range from feeding-related swelling to serious dropsy signs. Top-view scale appearance matters.

Key signs

Rounded belly, buoyancy trouble, reduced appetite, or stringy waste.
Raised scales visible from above may suggest a serious dropsy-like pattern.

First check: Check top view for pineconing and verify water/temperature.

Same-day concernRead guide

Other behavior and eye changes

Symptom guide

White Stringy Poop in Fish: What It Can Mean

A pale strand of waste can contain intestinal mucus, especially when little food is passing through. It can also accompany illness. What matters is whether it repeats and whether your fish is eating, maintaining weight, and behaving normally.

First check: Watch whether food is swallowed and check water quality.

Monitor closelyRead guide

Male betta fish in an aquarium, used as fin posture context. — Image: Gourami Watcher / CC BY-SA 3.0 / resized and cropped for layout

Symptom guide

Clamped Fins in Fish: Possible Causes and What to Check

Clamped fins are a broad stress sign. They matter most when paired with spots, rubbing, gasping, lethargy, or appetite changes.

Key signs

Fins held tight against the body instead of open.
Often appears with hiding, rubbing, appetite loss, or low activity.

First check: Check water and look for paired symptoms.

Monitor closelyRead guide

Guppies in an aquarium, used as feeding and behavior context. — Image: Schumi4ever / CC BY-SA 4.0 / resized and cropped for layout

Symptom guide

Fish Not Eating: Possible Causes and Next Checks

Appetite loss is common across many fish health problems. Recent tank changes, water tests, and visible symptoms help narrow the cause.

Key signs

Ignoring food, spitting food, hiding during feeding, or losing weight.
May pair with swollen belly, mouth damage, lethargy, or rapid breathing.

First check: Check water, bullying, mouth, belly, and breathing.

Monitor closelyRead guide

Neon tetra in an aquarium, used as general behavior context. — Image: Warrieboy / CC BY-SA 4.0 / resized and cropped for layout

Symptom guide

Lethargic Fish: Resting or Unwell? First Checks

Lethargy means your fish is less active or responsive than usual. Rest can be normal, but a sudden change, appetite loss, or difficult breathing needs attention. Start with water, temperature, and whether one fish or the whole tank is affected.

Key signs

Resting more than normal, hiding, bottom-sitting, or weak swimming.
Reduced appetite, clamped fins, dull color, or slow response.

First check: Check water, oxygen, temperature, and whether multiple fish are affected.

Same-day concernRead guide

Other behavior and eye changes

Fish Disease Identifier

Still not sure what your fish has?

Scan a photo in Fish Disease Identifier and get likely disease matches, possible causes, and next steps to consider.

Educational only. Not veterinary advice.

Browse disease guides