Several fish changed together
Check ammonia, nitrite, temperature, aeration, filter flow, and recent tank changes promptly. A tank-wide pattern often needs a water or oxygen response before disease comparison.
Fish symptom starting point
What's Wrong With My Fish?
If your fish suddenly looks or acts sick, first check whether breathing is affected and whether one fish or the whole tank has changed. Then test the water and compare the clearest visible symptom before assuming one disease.
Fish Disease Identifier
Start with one clear photo.
Scan your fish and compare likely disease matches, possible causes, and next checks to consider.
Educational only. Not veterinary advice.
Fast visible checks
- Breathing first: gasping, rapid gill movement, or several fish at the surface can be urgent.
- Whole tank or one fish: several affected fish make water, oxygen, heat, or contamination more likely.
- Visible clues: compare spots, swelling, damaged fins, red gills, fuzzy growth, posture, and appetite.
- Recent changes: review new fish, filter cleaning, medication, temperature swings, and missed maintenance.
Only one fish looks unwell
Compare appetite, breathing, posture, bullying, injuries, swelling, spots, fin edges, and progression. One affected fish can still have a water-related problem, so keep basic tests in the checklist.
Use a photo as supporting evidence
A clear side-view photo can help organize possible matches, but it cannot measure ammonia, oxygen, temperature, appetite, or how quickly the problem is spreading.
Escalate severe or unclear signs
Collapse, severe breathing distress, open wounds, rapid worsening, pineconing, or unexplained tank-wide decline should be reviewed by an aquatic veterinarian or experienced aquarium professional.
Match the visible sign
What does your fish look or act like right now?
Choose the clearest symptom first. Each guide compares possible causes, urgent water checks, and signs that need faster expert help.
Gasping at the surface
Start with oxygen, ammonia, nitrite, heat, and gill stress.
Check this symptomHiding or barely moving
Compare water stress, temperature, bullying, appetite, and visible illness.
Check this symptomWhite spots or marks
Separate salt-like grains from dusting, fuzz, flat patches, bubbles, and injuries.
Check this symptomTorn or frayed fins
Check nipping and injuries before comparing progressive fin rot.
Check this symptomSwollen or bloated belly
Compare diet, constipation, fluid buildup, eggs, and pineconing warning signs.
Check this symptomRed or inflamed gills
Test water promptly and compare oxygen, heat, irritation, and parasites.
Check this symptomSymptom guides
Start with white spots, torn fins, swelling, gasping, cloudy eyes, and behavior changes.
Disease guides
Compare likely matches such as ich, fin rot, dropsy, velvet, flukes, and bacterial problems.
Fish Disease Identifier app
Scan one clear fish photo and compare likely disease matches, possible causes, and next checks.
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.