So, you’ve caught the koi fever. You’ve studied the varieties—Kohaku, Showa, Sanke, Ogon—and you’re ready to bring home a few living jewels for your pond. But before you fall in love with the first fish that flashes its fins your way, you need to know what to look for. Not all koi are created equal—and choosing wisely can mean the difference between a pond full of beauty and one full of heartbreak (and vet bills).
Here’s your complete guide to spotting healthy, vibrant koi—from flawless fins to dazzling color patterns that make them the pride of any pond.
1. Start with Energy and Behavior
When you first walk up to a koi tank or pond, watch how the fish move. Healthy koi are curious, active, and alert. They glide gracefully but will often swim up to greet you (especially if they think food’s involved).
- ✅ Healthy koi: Swim smoothly, react to movement, and hold fins open like proud banners.
- ⚠️ Unhealthy koi: Lethargic, clamped fins, isolating in corners, or gasping near the surface.
Pro tip: Koi that eagerly follow your hand are not just hungry—they’re confident and well-adjusted. A shy fish hiding constantly might be sick, stressed, or new to the tank.
2. The Eyes Tell the Story
Koi eyes are like little windows to their soul—and their health. Look for clear, bright eyes that are symmetrical and alert.
- ✅ Healthy eyes: Transparent and reflective, showing curiosity.
- ⚠️ Unhealthy eyes: Cloudy, sunken, or bulging—potential signs of infection or poor water quality.
If the koi looks like it just pulled an all-nighter, move on. Clear eyes equal clear health.
3. Inspect the Skin and Scales (The Koi’s Canvas)
This is where the artistry of koi really shines. Whether it’s the pure white and deep red of a Kohaku or the shimmering gold of an Ogon, healthy koi skin should look clean, glossy, and vibrant. Scales should be tight and uniform, reflecting light evenly like polished armor.
- ✅ Healthy koi: Smooth, shiny skin with no blemishes or missing scales.
- ⚠️ Unhealthy koi: Raised scales, dull colors, ulcers, or white fuzzy patches (possible fungus).
Healthy koi literally glow—a combination of proper diet, genetics, and clean water. If the fish looks dusty or has uneven coloration, it might be under stress or recovering from illness.
4. Fins and Tail — The Flow of Elegance
The fins of a koi are its graceful banners, fluttering through the water like silk in the wind. They should be symmetrical, translucent, and fully extended when the koi swims.
- ✅ Healthy koi: Strong, open fins that fan out naturally; no fraying or discoloration.
- ⚠️ Unhealthy koi: Torn or clamped fins, red streaks (sign of bacterial infection), or visible damage from poor handling.
Pro tip: The dorsal fin (the one on top) should stand erect, not folded down. A droopy dorsal is the koi equivalent of bad posture—it often signals stress or illness.
5. Body Shape and Proportion
A koi’s body should have the smooth, torpedo-like shape of a creature built for gliding. Avoid koi that look too skinny, bloated, or unevenly shaped.
- ✅ Healthy koi: Balanced body, full yet streamlined, evenly proportioned from head to tail.
- ⚠️ Unhealthy koi: Lopsided, pinched behind the head, or distended belly—possible internal issues or parasites.
Also check for symmetry—especially in patterned koi like Sanke or Showa. While no koi is perfectly symmetrical, evenly distributed colors and markings are highly desirable.
6. Evaluate the Colors and Patterns
This is where koi become living art. Each variety has its own ideal coloration and pattern balance. Here’s what to look for in some of the most popular types:
- Kohaku: Pure white base with bold red markings. The edges of the red patches (hi) should be clean and crisp, with no bleeding into the white.
- Showa: Black base with red and white patterns. The best Showa have balanced color across the body and dramatic contrast.
- Sanke: White base with red and black markings—but the black (called sumi) should never appear on the head. Look for elegant placement and symmetry.
- Ogon: Solid metallic gold or platinum sheen. The color should be uniform and gleam like polished metal.
- Asagi: Blue-gray net pattern across the back with red-orange on the belly and fins. Look for even, tight scales and calm, soft tones.
Healthy koi have colors that appear deep and consistent, not faded or patchy. Pale hues or sudden color loss may indicate stress, illness, or poor genetics.
Pro tip: Lighting can deceive you—always check koi in natural daylight if possible. A Sanke’s bright reds might look stunning under indoor bulbs but less vibrant outside.
7. Breathing and Gills
Koi are surprisingly expressive when it comes to breathing. Watch how they move their gills and mouths.
- ✅ Healthy koi: Slow, steady breathing with gills moving smoothly.
- ⚠️ Unhealthy koi: Rapid gill movement, gasping at the surface, or flared gills—possible signs of low oxygen or gill parasites.
Healthy koi glide effortlessly without gasping or surfacing frequently. If they seem to struggle or breathe unevenly, something’s not right.
8. Check the Environment
Even the healthiest koi can’t thrive in poor conditions. Observe the water in the holding tank or pond before buying:
- ✅ Good environment: Clear, well-aerated water with active filtration. Koi swim calmly and interact normally.
- ⚠️ Bad environment: Cloudy water, algae bloom, floating debris, or multiple sick fish in one tank—walk away immediately.
Pro tip: A breeder or dealer who takes pride in their water quality likely takes pride in their koi. A clean pond reflects a clean operation.
9. Ask the Right Questions
Don’t be shy! A good koi seller will welcome your curiosity. Ask about:
- Water parameters (pH, KH, ammonia, nitrite)
- Feeding schedule and diet
- Quarantine procedures for new imports
- Age and size expectations for each koi
If a seller can’t answer basic questions, that’s your cue to look elsewhere. You’re not just buying fish—you’re investing in living art, and you deserve transparency.
Healthy koi are the foundation of a beautiful, thriving pond. Look for energy, symmetry, and vibrancy in every fish you buy. Whether you’re eyeing a fiery Showa, a serene Asagi, or a golden Ogon that gleams like sunlight itself, true health will always shine through.
In short: watch how they swim, study their colors, and trust your gut. A healthy koi will speak to you through its vitality, balance, and beauty—and when you find the right one, you’ll know it’s meant to be part of your pond’s story.