How Big Do Arowana Get? Growth Rate, Adult Size and Tank Planning
An arowana bought at 6-8 inches can outgrow a 55-gallon tank before its first birthday. Depending on species, adults range from about 2 feet to nearly 4 feet long, and getting there takes only a few years of fast, steady growth. This guide breaks down realistic growth rates, adult sizes by species, and the tank upgrades you should budget for before you bring one home.
Why Arowana Growth Catches New Owners Off Guard
Most arowana sold in stores are juveniles between 3 and 8 inches — a size that fits comfortably in almost any tank. That's the problem. Nothing about a small juvenile hints at what's coming.
Under good feeding and water conditions, arowana commonly gain roughly 1-2 inches of length per month during their first year. A fish bought at 6-10 inches can realistically reach 18-24+ inches within 12 months. Growth isn't perfectly linear — it tends to be fastest in the first several months and then tapers as the fish gets larger — but even a conservative pace adds up quickly.
The most rapid growth happens in the first 2-3 years. After that, length gain slows sharply, though the fish may continue to fill out and thicken for several more years even after it's essentially reached adult length.
Diet, water temperature, and available swimming space all influence how fast an individual fish grows, so treat any monthly figure as an estimate rather than a guarantee.
Adult Size by Species
Not all arowana get equally large, and lumping every species into one "arowana" size estimate is a common mistake. Here's how the US-relevant species compare as adults.
| Species | Typical adult length | Exceptional specimens | Approx. adult weight |
|---|---|---|---|
| Silver arowana | ~3 ft (36 in) | 3.5-4 ft | 10-15+ lbs |
| Black arowana | ~3 ft (36 in) | up to ~3.5 ft | 10-15+ lbs |
| Jardini / Australian arowana | ~2 ft (24 in) | 30-36 in (mostly in the wild) | Notably lighter-bodied than silver/black |
| Asian arowana (dragon fish) | 3-4 ft in native range | — | — |
A note on silver arowana claims: you'll see everything from "3 feet" to "4.5 feet" quoted for adult silvers. A realistic planning range is 3-3.5 feet for typical captive adults, with exceptionally well-fed specimens approaching 4 feet. When sizing a permanent tank, plan for the larger end rather than the average.
Jardini owners, take note: because most general care advice defaults to silver arowana, jardini keepers are often told they need a 300-gallon tank they don't actually need. At roughly 24 inches adult length, jardini-type arowana are a meaningfully smaller commitment than silver or black arowana.
Asian Arowana: A Legal Note for US Buyers
Asian arowana (Scleropages formosus, including all the "dragon fish" color forms) are CITES-protected and cannot be legally imported or sold in the United States. This is worth stating plainly because a lot of general care content is written as though any hobbyist can simply buy one — in the US market, that isn't an option. If you want an arowana-type fish stateside, your realistic choices are silver, black, or jardini arowana.
Tank Upgrade Timeline: Matching Tank Size to Fish Length
Rather than a single "arowana tank size" number, it helps to think in stages tied to the fish's length. Because arowana are fast, surface-dwelling swimmers, horizontal length and width matter far more than tank height — a tall tank wastes water volume without giving the fish anything useful.
| Fish length | Recommended tank | Notes |
|---|---|---|
| Under ~12 in (juvenile) | 55-75 gallons | Workable short-term; expect to outgrow it within months |
| 12-20 in (growing sub-adult) | 125-180 gallons | First real upgrade trigger |
| 20-24 in (young adult) | 180 gallons minimum | Final tank for jardini-type; stepping-stone for silver/black |
| 24-30+ in (adult silver/black) | 250-300+ gallons | 250 gal as the floor, 300+ as the comfortable standard |
A practical way to plan: upgrade around 12 inches, upgrade again around 20 inches, and have the final tank ready by 24-30 inches — well before the fish actually needs it, not after.
Why Width and Depth Matter More Than Height
Arowana are strong, fast horizontal swimmers that spend most of their time near the surface. Tank guidance for this species should prioritize:
- Length, so the fish has real swimming distance
- Width of at least 24 inches, so it can turn around without stress or bending
- Height of 24-30 inches, which is plenty — arowana rarely use the lower half of a very tall tank, so extra height is mostly wasted water volume and cost
The 180-Gallon Tank, Explained
The 180-gallon glass tank is a frequent reference point in arowana planning because of its footprint: roughly 72 x 24 x 24-25 inches (6 ft x 2 ft x 2 ft), weighing about 300-340 lbs empty before water, substrate, or equipment.
For a jardini-type arowana topping out around 24 inches, a 180-gallon tank can be a genuine long-term, permanent home. For a silver or black arowana headed toward 3+ feet, the same tank is only a stepping-stone — useful during the sub-adult stage, but not sufficient once the fish reaches full adult length. You can browse glass tanks sized for each stage of that upgrade path.
Water Parameters and Filtration for a Fast-Growing, Heavy Eater
Arowana aren't fussy about exact numbers, but they do best within a consistent range:
- Temperature: 75-85°F (24-29°C)
- pH: 6.0-7.5 (soft, slightly acidic to neutral)
- Hardness: low, roughly 1-8 dGH/dKH
- Water changes: about 25% weekly, given the heavy bioload
Because arowana are large, messy, carnivorous eaters, filtration is frequently underestimated. A tank this size needs robust mechanical and biological filtration turning over substantially more water volume per hour than a typical community setup — undersized filtration is one of the fastest ways to end up fighting ammonia and nitrite spikes in a 200+ gallon tank. Pairing a canister or sump-style system with strong mechanical prefiltration, and keeping up with the weekly water-change schedule, matters as much as tank size itself. FishyHub's filters and external filters sections are worth browsing when sizing equipment to a tank this large.
Feeding an Arowana as It Grows
Arowana are strictly carnivorous, and their diet should shift as they grow:
- Juveniles: fed 2-3 times per day
- Adults: once daily, or every 1-2 days
A varied diet — feeder fish (used sparingly, since they carry disease risk), shrimp, crickets, mealworms, earthworms or nightcrawlers, plus a quality carnivore pellet or a gel food — keeps nutrition balanced. Overfeeding, especially fatty feeder fish, is a common contributor to obesity and fatty liver problems in captive arowana, so portion control matters more than volume. You can compare carnivore-formulated options in food & supplements.
Lifespan
Given reasonable care, arowana commonly live 10-15 years in captivity, and well-maintained fish have been reported reaching 15-20+ years. That lifespan is worth sitting with before buying: this is a multi-decade commitment housed in a tank that will eventually hold several hundred gallons of water.
Common Mistakes to Avoid
- Buying without a plan for the 250-300 gallon endpoint. This is the single most cited arowana mistake — starting a fish that will need a tank most homes don't already have room or budget for.
- Undersized filtration. Arowana produce a heavy bioload; filtration should be sized generously, not to the tank's minimum recommendation.
- Light-duty or missing lids. Arowana are reliable jumpers from a young age. A secure, weighted lid is mandatory at every life stage, not just once the fish is large.
- Bright, direct overhead lighting. Constantly looking upward and down at overhead light has been linked to "drop-eye" (downturned eye) syndrome. Diffused or lower-intensity lighting, plus feeding from varied depths and positions, is generally recommended to reduce the risk.
- Risky tankmates. Fish small enough to be eaten will eventually become food; overly aggressive tankmates can damage an arowana's sensitive barbels and scales.
- No exit plan. Because full-grown arowana are so large, rehoming one that's outgrown its setup is genuinely difficult. It's worth checking with local aquarium clubs or stores about interest in advance, rather than scrambling once the fish is already at adult size.
If you're weighing an arowana against other large freshwater fish with different space and lifespan requirements, FishyHub's monster fish category is a useful place to compare options before committing to a tank size.
Frequently Asked Questions
How fast do arowana grow in the first year?
Roughly 1-2 inches per month is typical with good food and warm, clean water. A juvenile can more than double or triple in length within its first 12 months, though the pace slows as the fish gets larger.
What is the maximum size an arowana can reach?
It depends on species: jardini-type arowana top out around 24 inches, while silver and black arowana commonly reach 36-48 inches, and occasionally more in exceptional cases.
When do arowana stop growing?
Growth slows sharply after about 2-3 years, by which point most arowana are near their full length. Some slow filling-out and thickening can continue for a while after that.
What size tank does a baby arowana need to start?
A 55-75 gallon tank works for the first several months. Plan the next upgrade well before the fish approaches that tank's limits, rather than waiting until it's visibly cramped.
Can arowana live in a 180-gallon tank permanently?
Yes for jardini-type arowana, which top out around 24 inches. No for silver or black arowana — a 180-gallon tank is a useful stepping-stone stage for them, but they need to graduate to 250-300+ gallons as full adults.
Why is my arowana's eye drooping?
This is usually linked to bright overhead lighting combined with the fish's habit of looking down for food, a pattern associated with "drop-eye" syndrome. Diffused or lower lighting and feeding from varied depths can help reduce the risk.
Are Asian (dragon) arowana legal and available in the US?
No. Asian arowana are CITES-protected and cannot be legally imported or sold in the United States. US hobbyists interested in this fish should look at silver, black, or jardini arowana instead.
How much does an adult arowana weigh?
Large species like silver and black arowana commonly reach 10-15+ pounds at full adult size, with weight scaling alongside their 3-4 foot length.
Before buying, match the species to a tank size you can realistically commit to for over a decade. Browse current stock in freshwater livestock to compare arowana against other large freshwater species while you plan your setup.
