Not everyone who builds an aquaponics system wants to eat their fish — and that’s perfectly fine. Ornamental fish offer real advantages in aquaponics, from ease of care to visual appeal, and they produce the same nutrient-rich water that grows plants as effectively as edible species. Here’s what you need to know about using ornamental fish in an aquaponics system.
Can Ornamental Fish Really Power an Aquaponics System?
Yes, absolutely. The fundamental driver in aquaponics is fish waste — specifically ammonia from fish excretion — which beneficial bacteria convert into nitrates that plants absorb. Ornamental fish produce exactly the same waste as edible species. Goldfish, koi, and other ornamental varieties have been used successfully in aquaponics systems around the world, including some of the most beautiful backyard setups in Australia.
What Are the Best Ornamental Fish for Aquaponics?
Goldfish
Goldfish are arguably the ideal aquaponics fish for home growers not interested in eating their stock. They’re extremely hardy, tolerant of a wide temperature range (10–30°C), inexpensive to purchase, readily available, and produce good volumes of waste relative to their body size. Common and comet goldfish are more robust than fancy varieties for aquaponics purposes.
Stocking density: 1–2 fish per 20 litres of tank water is a conservative starting point.
Koi
Koi are stunning fish that create a beautiful visual centrepiece for a backyard aquaponics setup. They’re also prolific waste producers, making them effective nutrient generators. Koi can live for decades and grow large, so plan for adequate tank volume — a mature koi needs at least 1,000 litres per fish for a quality life.
Note: Koi can be expensive, so consider starting with common carp or feeder koi while you establish your system.
Jade Perch
While technically an edible species, jade perch are so visually striking (they develop beautiful blue-green colouration) that many growers keep them purely for aesthetics. They’re also native to Australia, which avoids the biosecurity complications of exotic species.
Murray Cod
Murray cod are another Australian native that can be kept ornamentally. They’re powerful, impressive fish — though they require careful management as they can be aggressive and will eat smaller tank mates.
Tropical Ornamentals (Indoor/Greenhouse Systems)
In heated indoor or greenhouse systems, larger tropical ornamentals like cichlids, large tetras, and even some decorative catfish species can be used. These require more stable temperatures and careful water quality management but can create spectacular indoor living systems.
What Are the Advantages of Ornamental Fish in Aquaponics?
No Harvest Pressure
With edible fish, you eventually face the practical and emotional challenge of harvesting. With ornamental fish, you build long-term relationships with animals that can live for years or decades. Many backyard growers find this deeply satisfying.
More Design Freedom
Ornamental aquaponics systems can be designed as much for visual beauty as for productivity. Koi ponds with integrated grow beds, goldfish wall gardens, and indoor aquarium-aquaponics combinations create stunning living installations that double as food production systems.
Lower Regulatory Complexity
In some Australian states, keeping certain edible native fish species requires aquaculture permits. Ornamental goldfish and koi typically face fewer regulatory restrictions for hobby growers. Always check with your state’s Department of Primary Industries before setting up any fish-keeping system.
What Are the Limitations of Ornamental Fish for Aquaponics?
No Fish Harvest
The obvious trade-off is that you won’t be harvesting fish for food. If dual protein and vegetable production is your goal, ornamental-only systems don’t deliver that aspect of the aquaponics promise.
Waste Load Management
Koi in particular produce large volumes of solid waste. Ensure your biofiltration and solid waste removal systems are adequate for your stocking density. Regular partial water changes and good mechanical filtration (swirl filters or settlement tanks) help manage the waste load before it reaches your grow beds.
Combining Ornamental and Edible Fish
Some growers run hybrid systems — koi or goldfish in a decorative pond component, connected to grow beds, alongside a separate grow-out tank with edible species. This captures the visual appeal of ornamental fish while maintaining the option to harvest food fish separately.
Frequently Asked Questions
Are goldfish as effective as tilapia for aquaponics nutrient production?
Goldfish produce sufficient waste to support plant growth, but tilapia and other edible species are typically stocked at higher densities, producing more nutrients per litre of tank volume. For a home system growing herbs and leafy greens, goldfish are entirely adequate.
Can I use fancy goldfish (telescope, ryukin, etc.) in aquaponics?
Fancy goldfish are more delicate than common varieties and less tolerant of variable water quality. They can work in a well-established, stable system but aren’t recommended for beginners. Common or comet goldfish are far more robust.
Do ornamental fish in aquaponics need the same water quality as edible fish?
Yes — the core parameters (ammonia near zero, nitrite near zero, pH 6.8–7.4, adequate dissolved oxygen) apply regardless of species. Koi can tolerate slightly higher nitrate levels than sensitive species, but consistent good water quality is always the goal.
How many goldfish do I need to grow vegetables in aquaponics?
For a standard media bed (approximately 60 x 120 cm), 5–10 adult goldfish in a 200–400 litre tank typically provides adequate nutrients for good plant growth.
Can I keep koi in a small backyard aquaponics system?
Koi need significant space — at least 1,000+ litres per adult fish for good welfare. Smaller backyard systems are better suited to goldfish. Koi work well in larger pond-based aquaponics setups with 3,000+ litres of water volume.
Thinking about building a beautiful aquaponics system — whether with ornamental fish or edible species? Get the complete design and build guide here and create a system that fits your goals.