How do I tell if a fish at the store is healthy before I buy it?
When: Every time you shop for a new fish, before it leaves the store
Short answer: Watch the fish for a few minutes before you buy it — a healthy fish swims normally, breathes evenly, has intact fins and clear eyes, and eats readily when the store feeds it. Any white spots, rapid breathing, scratching against rock, clamped or tattered fins, or a refusal to eat means walk away, even if it's a fish you've wanted for a long time.
The details
Check the store first. Clean, algae-free tanks, no dead fish sitting in a display, and staff willing to talk about their quarantine process are all good signs. If tanks share one filtration system, a sick fish in one tank can mean every "healthy-looking" fish sharing that water is at risk too — skip the whole system, not just the obviously sick tank.
Watch its behavior. A healthy fish swims upright without struggling to stay level, breathes evenly (compare its gill rate to tankmates), and isn't gasping at the surface or glued to the bottom. Watch for flashing — darting and scratching itself against rock, sand, or the glass — which signals external parasites. Fins should be held erect, not clamped down.
Look for visible disease or injury. White spots (ich or velvet), red patches or streaks, open wounds, torn or shredded fins, cloudy or swollen eyes, fungus-like growths, bumps, and a swollen or concave (sunken) belly are all reasons to pass.
Ask them to feed it. A healthy fish readily takes prepared foods (pellets or flakes). Refusal to eat when offered food is one of the strongest predictors that a fish won't make it — don't buy a fish that won't eat, hoping it will "settle in" at home.
Prefer captive-bred stock when it's available. Captive-bred fish generally ship and survive better, tend to be less aggressive, and carry lower disease risk than wild-caught animals.
The numbers
| Check | What you want |
|---|---|
| Breathing | Even, matches tankmates — not rapid/labored |
| Fins | Erect and intact — not clamped or tattered |
| Eyes | Clear — not cloudy or swollen |
| Body | No white spots, red streaks, or visible wounds |
| Feeding | Readily eats when the store feeds it |
| Sourcing | Captive-bred preferred when available |
Common mistakes
- Buying on looks alone without watching the fish for a few minutes first.
- Skipping the "ask them to feed it" step.
- Buying a fish from a tank that shares filtration with a visibly sick tank.
- Making an impulse buy on a high-risk fish (wild-caught rarity, no feeding response).
When to worry
- Normal: a little shyness or hiding right after being moved to a store display tank — species-dependent.
- Worry: any white spots, refusal to eat, rapid gilling, or flashing. Leave it at the store — one sick fish can bring disease into a whole tank.
What's next
Once you've picked a healthy fish, it still needs a careful transition into your water: how-to-drip-acclimate-new-livestock.
- Any white spots on the body or fins (possible ich)
- Rapid/labored breathing, gasping at the surface, or darting/scratching against rock (flashing)
- Refuses to eat when the store feeds it
- Cloudy or swollen eyes, red streaks, sunken belly, or tattered/clamped fins
- AlgaeBarn — How to Choose Healthy Saltwater Fish
- Bulk Reef Supply — 8 Rules for Picking Out New Saltwater Fish (Ep. 33)
- Coral Reef Knowledge Base (internal) — Fish Health & Disease