The fish species you stock determines half of how your aquaponic system runs. Water temperature requirements, feed cost, growth rate, oxygen demand, stocking density, and even the system layout shift based on what swims in the tank. This article compares the four common aquaponic fish species (tilapia, trout, catfish, and ornamental goldfish or koi) on the dimensions that matter and helps you pick the right one for your climate, system size, and tolerance for fish husbandry.
Tilapia, the default choice
Tilapia is the most common aquaponic fish for good reason. The fish tolerates a wide range of water quality, grows fast, reaches harvest size in under a year, and is comfortable to eat with mild white meat similar to bass.
Water temperature: 75 to 86 F is ideal. Below 65 F tilapia stop eating and stop growing. Below 55 F they die. Above 90 F dissolved oxygen drops to dangerous levels.
Growth rate: Fingerling to 1 lb harvest in 8 to 12 months on commercial floating pellet feed.
Feed conversion ratio: About 1.5 to 1.7 lb of feed per lb of fish gained. Best in class for warm water species.
Stocking density: 0.5 to 1 lb of fish per gallon of tank water in a well-aerated system. A 200 gallon tank holds 100 to 200 lb of fish at full grown weight.
Where they fail: Indoor systems in cold climates without supplemental tank heating run too cool for tilapia. Outdoor systems north of zone 7 cannot keep tilapia alive in winter without insulated tanks and water heaters that drive electricity costs sky high.
Legal note: Tilapia are an invasive species in some southern US states and farming them at home requires a permit in Texas, Florida, Louisiana, Arizona, and a few others. Check your state regulations before buying fingerlings.
Trout, the cool water option
Rainbow trout is the cool climate counterpart to tilapia. The fish wants cold, well-oxygenated water and rewards the grower with delicious meat at harvest.
Water temperature: 50 to 65 F is ideal. Above 70 F trout stop eating. Above 75 F they begin to die within hours. Below 40 F they slow growth dramatically.
Growth rate: Fingerling to 1 lb harvest in 12 to 18 months. Slower than tilapia because cooler water means slower metabolism.
Feed conversion ratio: About 1.2 to 1.4 lb of feed per lb of fish gained. Excellent.
Stocking density: 0.3 to 0.5 lb of fish per gallon in a well-aerated system. Trout demand more dissolved oxygen than tilapia, which caps density.
Where they fail: Trout cannot survive in warm climates without an active chiller, which is expensive and noisy. Indoor systems with LED grow lights tend to run warm, which makes trout a poor fit for most indoor setups. Outdoor systems in temperate zones with cool basement or shaded outdoor placement work well.
Sourcing: Many state fish hatcheries sell rainbow trout fingerlings for $2 to $5 each in spring stocking windows. The fingerlings must be ordered months in advance for spring delivery.
Catfish, the resilient option
Channel catfish tolerates poor water quality better than any other common aquaponic fish. The fish is forgiving of beginner mistakes, grows reasonably fast, and produces good meat at harvest.
Water temperature: 65 to 85 F is ideal. Tolerates 55 to 90 F without serious problems.
Growth rate: Fingerling to 1 lb harvest in 10 to 14 months.
Feed conversion ratio: About 1.6 to 1.8 lb of feed per lb gained.
Stocking density: 0.5 to 0.8 lb per gallon. Catfish handle higher ammonia tolerance than tilapia or trout, which gives the bacterial colony more margin for error during system cycling.
Where they fail: Catfish are bottom feeders and dislike bright light. Most home aquaponic tanks have some surface light from grow lights or windows, and the catfish cluster in shaded corners. Production density suffers compared to tilapia in the same tank. They also have an earthy flavor profile that some growers dislike.
Best use: Beginner growers and growers in regions where tilapia farming is restricted by law.
Goldfish and koi, the ornamental option
For growers who want plant production without slaughtering fish, goldfish and koi are the practical choice. Both produce ammonia at rates similar to edible fish, tolerate wider temperature ranges, and live for many years.
Water temperature: 50 to 80 F is fine for both. Wide tolerance is a major advantage in outdoor systems with seasonal swings.
Growth rate: Not relevant since they are not harvested.
Stocking density: 0.5 to 1 lb per gallon for goldfish, 0.3 to 0.5 lb for koi (koi grow larger and need more swimming room).
Where they fail: No meat production. The fish cost increases over time as koi can outgrow the tank and need rehoming.
Best use: Growers who want the closed-loop biology without the commitment of an annual fish harvest, growers with kids who name the fish, and growers who just want pretty fish.
Stocking math by system size
A 50 gallon system supports 6 to 10 small fish (tilapia fingerlings, goldfish) and 10 to 20 sq ft of grow bed. Too small for trout because oxygen volume is too low.
A 200 gallon system supports 30 to 50 fish to harvest size and 60 to 100 sq ft of grow bed. The standard hobby aquaponic scale.
A 500 gallon system supports 80 to 150 fish and 150 to 300 sq ft of grow bed. The standard small commercial scale, often built from an IBC tote setup or a fiberglass aquaculture tank.
Picking the right fish for your situation
Choose tilapia if you live in a warm climate or run an indoor system, want fast growth and the highest plant production rate, and your state permits tilapia.
Choose trout if you live in a cool climate or have a cool basement, do not mind a slower harvest cycle, and want the highest quality fish meat.
Choose catfish if you are new to aquaponics, want the most forgiving species, or your state restricts tilapia.
Choose goldfish or koi if you want plant production without the harvest step, or if this is a family system where slaughtering fish is not on the agenda.
See the methodology page for our aquaponic testing protocol. Choosing fish is half the system design; pair this article with our aquaponics vs hydroponics comparison and our hydroponic systems guide.
Frequently asked questions
Tilapia vs trout for aquaponics: which is the better choice?+
Tilapia for warm climates, trout for cool climates. Tilapia thrive in 75 to 86 F water and grow fastest in that range. Trout thrive in 50 to 65 F water and refuse to eat above 70 F. If your indoor aquaponic system runs at 72 to 78 F (typical with grow lights), tilapia is the right choice. If you run an outdoor system in a temperate region with cool basement water, trout works. Mixing the two species in one system is not viable because their temperature requirements do not overlap.
How long until aquaponic fish are big enough to eat?+
Tilapia reach 1 lb harvest weight in 8 to 12 months from fingerling. Trout reach the same size in 12 to 18 months because their growth rate slows in cooler water. Catfish reach 1 lb in 10 to 14 months. Growth is roughly linear with feed temperature and water quality. Cold water fish in heated tanks lose to fish suited to that water; trout in 75 F water grow slowly and stress easily, while tilapia in 60 F water barely grow at all.
Can I keep goldfish or koi in an aquaponic system?+
Yes, but they are ornamental rather than edible. Goldfish and koi tolerate a wide temperature range (50 to 80 F), produce ammonia at similar rates per pound to food fish, and are cheap fingerlings (under $2 each). The downside is they live 10 to 20 years and are not eaten. For a grower who wants the plant production without the slaughter step, goldfish or koi are the easy answer. They also tolerate beginner mistakes better than tilapia or trout, which makes them a forgiving choice for the first system.
What is the fish to plant ratio?+
Roughly 1 lb of fish supports 1 to 2 square feet of grow bed for leafy greens, or 0.5 to 1 square foot for fruiting plants. A 200 gallon fish tank holding 30 fish at 1 lb average supports 30 to 60 sq ft of leafy green grow bed. The ratio shifts as the fish grow: a tank of fingerlings supports less plant area than the same tank with adult fish. Most systems target the mature ratio and run with extra biofilter capacity in the early months.
Can I eat aquaponic fish safely?+
Yes, assuming the system has been managed cleanly. Aquaponic fish eat commercial pellet feed and live in monitored water. The meat quality is at least as good as supermarket farmed fish, often better because the water is fresher. The safety concerns are: a system that received pesticide-treated water (do not spray your plants with anything not labeled aquaponic-safe), a system with mineral buildup or contaminated feed, and undercooked fish. Cook to 145 F internal temperature. Most home aquaponic harvests are cleaner than supermarket fish.
Morgan Davis
Morgan Davis writes for The Tested Hub.