When guppy tails look damaged, people often jump straight to “fin rot.” Sometimes it is fin rot — but many times it’s nipping, stress tears, or mechanical damage from décor and filter intakes. The reason this matters is simple: the fix depends on the cause. Medication won’t stop a bully, and removing a bully won’t fix ammonia burn. If you can tell these three apart, you’ll solve fin problems faster and keep the tank more stable.
Fin nipping (behavioural)
- damage often looks like small bites or ragged edges
- you may see chasing at feeding time
- one or two fish often get hit the worst
Fin tears (mechanical)
- clean “splits” or straight tears
- often linked to sharp decor, rough nets, or strong flow
- edges look clear rather than fuzzy
Fin rot (bacterial breakdown)
- edges look fuzzy, melting, or progressively receding
- often worsens over days
- commonly linked to chronic poor water or stress
Best first response
- test water (ammonia/nitrite must be 0)
- stabilise routine and improve cleanliness
- observe behaviour for nipping
- inspect decor and flow for tear risks
In many cases, once you remove the cause and keep water clean, guppy fins regrow surprisingly well. Diagnosis is the difference between fighting symptoms and fixing the system.
