Group of colourful koi carp swimming among green lily pads in a clear outdoor pond

Choosing Pond Fish: Koi, Goldfish & More

Creating a thriving garden pond starts with choosing the right fish. Whether you dream of vibrant koi gliding through crystal-clear water or a peaceful display of shimmering goldfish, selecting suitable species is key to a healthy, balanced pond.

At Birchwood Aquatic Centre, we’re here to help you find the perfect pond fish for your space, water conditions, and experience level.

Popular Pond Fish Species

Koi Carp

Koi are the kings of garden ponds — stunning, intelligent, and full of personality.

  • Ideal for: Larger ponds (over 1,000 gallons)
  • Growth: Up to 2–3 feet
  • Care: Require strong filtration, good aeration, and regular feeding
  • Varieties: Kohaku, Sanke, Showa, Butterfly Koi, and more

Koi thrive in stable, well-filtered environments and can live for decades when cared for properly.

Goldfish

A classic choice that’s hardy and colourful. Perfect for smaller or medium ponds.

  • Ideal for: Beginners and smaller ponds
  • Growth: 10–12 inches
  • Care: Low-maintenance and adaptable to UK climates
  • Varieties: Common, Comet, Shubunkin, Sarasa, and Fantail

Goldfish can live harmoniously in groups and add instant movement and charm to your pond.

Orfe (Golden, Blue & Albino)

Fast-swimming and active, Orfe are perfect for adding liveliness to your pond.

  • Ideal for: Ponds with good oxygenation and surface movement
  • Growth: Up to 18 inches
  • Care: Prefer to be kept in groups of five or more

They’re beautiful, sociable fish that help keep your pond lively and balanced.

Tench (Green or Golden)

Green and golden tench resting near the bottom of a natural garden pond.

Tench are peaceful bottom dwellers that help clean up leftover food.

  • Ideal for: Natural or wildlife ponds
  • Growth: Up to 12 inches
  • Care: Hardy and excellent for mixed ponds

They stir up the sediment gently, helping to keep debris from building up.

Other Pond Fish Options

For something different, consider:

  • Rudd: A shimmering native species, great for movement at the surface
  • Sturgeon/Sterlets: Striking but only for large, well-filtered ponds with high oxygen levels
  • Minnows & Sticklebacks: Ideal for natural or wildlife ponds without large predators

Mixing Species Safely

Not all pond fish are compatible. Larger koi may accidentally swallow small goldfish or minnows, and fish with different temperature or oxygen needs may struggle together. Before mixing species, check:

  • Pond size & depth
  • Filtration capacity
  • Water temperature & oxygen levels
  • Feeding requirements

Our team can advise you on the best species combinations for your pond setup.

How Many Fish Can You Keep?

Pond shape, filtration, and oxygenation make a big difference.

Tips for Healthy Pond Fish

  • Perform weekly partial water changes during warm months
  • Avoid overfeeding – feed only what fish consume in 2–3 minutes
  • Maintain good aeration and use pond plants to improve oxygen levels
  • Test water regularly for ammonia, nitrite, and pH
  • Quarantine new fish before adding to your main pond

Need Expert Advice?

Our staff at Birchwood Aquatic Centre are passionate pond keepers too. We’ll help you choose fish suited to your pond’s size, setup, and maintenance level — ensuring long-term success and a beautiful display all year round.

Visit us in Swanley, Kent, for expert one-to-one advice on pond design, filtration, and fish care.

Birchwood Aquatic Centre, London Road, Swanley, Kent Call us or visit for expert fish health advice. Healthy fish start with healthy water — we’re here to help every step of the way.


Frequently Asked Questions


Yes — koi and goldfish can share a pond as long as it’s large enough, well-filtered, and the koi aren’t big enough to swallow the smaller goldfish. Both species enjoy similar temperatures and feeding habits.


Ideally at least 1 metre (3 feet) deep to protect them from temperature changes and predators. Deeper ponds also help koi overwinter safely.

Goldfish, Shubunkins, or small varieties of Sarasa Comets are perfect for smaller ponds. Avoid koi or orfe, as they grow large and need more space.


It’s not recommended. Native species may carry parasites or diseases that ornamental fish aren’t used to, and they often have different feeding habits.


Maintain clean, well-oxygenated water, feed appropriately, and test your water regularly. In winter, avoid disturbing the pond’s natural ice layer too much—use a pond heater or air stone instead.


Yes — even for goldfish, filtration helps remove waste, maintain clear water, and support beneficial bacteria that keep your pond balanced.


With good care, goldfish can live 10–20 years, and koi can live 25–50 years or even longer.


Only when water quality is stable. Always quarantine new fish for at least two weeks to prevent spreading disease to your existing stock.

Related Guides