Big Fish in Aquariums: From Alligator Gar to Arapaima

Keeping large and exotic fish in home aquariums has become increasingly popular among aquarists. While beginners often start with small community fish, the challenge and prestige of maintaining monster fish is hard to resist. This guide will provide an overview of aquariums’ most popular big fish, from prehistoric-looking Alligator Gars to the legendary Arapaima of the Amazon.

Key highlights include:

  • Big fish species like Arapaima, Alligator Gar, Stingrays and Catfish
  • Housing considerations such as tank sizes and water parameters
  • Ethical factors for avoiding “big fish, small tank” situations
  • Biology, including predatory behavior and community compatibility
  • Legal restrictions regarding native sport and exotic game fish
  • Illusion factors making fish appear even larger in home aquariums
  • Options for tank upgrades and responsible rehoming
  • Discussion of the world’s largest public and private fish exhibits

Types of Big Fish for Aquariums

Many aquarists are surprised by the diversity of large fish species that can be kept in home aquariums. Here are some of the most popular options:

Alligator Gar

The prehistoric-looking Alligator Gar is one of the most coveted monster fish among advanced aquarists. With elongated bodies covered in hard ganoid scales and snouts filled with sharp teeth, they live up to their fearsome appearance.

Native to the freshwaters of the southern United States, Alligator Gars can grow over 10 feet long in the wild. With proper care and a large enough tank, they can reach lengths of 4-6 feet in captivity. Despite their intimidating looks, Alligator Gars are relatively peaceful fish when kept with tank mates too big to swallow.

These primordial giants prefer murky, slow-moving waters in nature. Replicating their natural biotope with a fine sandy substrate, driftwood, and low lighting is key to their well-being in aquariums. Their unique physiology also requires specific water parameters – temperatures between 75-82°F, pH of 7.0-7.5, and moderate hardness.


Hailing from the Amazon River basin, Arapaima are legendary giants capable of exceeding 10 feet long and over 400 pounds. Due to complex breeding behaviors, nearly all Arapaima in the aquarium trade are wild-caught.

Arapaima are apex predators with uniquely adapted mouths allowing them to gulp air at the surface. This obligate air-breathing behavior must be accommodated in captivity. Though juveniles can be kept in large aquariums over 500 gallons, adults require massive custom-built ponds or tanks over 5,000 gallons.

Despite their demanding needs and predatory instincts, Arapaima are highly coveted trophy fish among elite aquarists. Their streamlined torpedo-shaped bodies and prehistoric grandeur captivate all fortunate enough to observe them in aquariums. Legal regulations also restrict Arapaima ownership in many areas.

Catfish and Suckermouth Catfish

Armored catfish comprise a diverse group of scaleless bottom-dwelling fish. Many species are suitable for large home aquariums, the most popular being Plecos, Dorads, and shovelnose catfish.

Plecos, also called suckermouth catfish, are ubiquitous in the aquarium trade thanks to their docile nature and appetite for algae. Though juveniles stay under 12 inches, large species like Common Plecos can exceed 2 feet in length given adequate space.

Doradids, known as thorny or talking catfish, are another popular choice. Species like Leopard Dorads have a maximum length around 14 inches and are suitable for medium to large community tanks. They are easy to care for but use their sharp spines in self-defense.

Shovelnose catfish have streamlined bodies and flattened shovel-shaped snouts. Some species like Redtail Catfish can eclipse 3 feet in home aquariums. Their active swimming makes them better suited for large open tanks.

Giant Snakehead and Jaguar Cichlid

Though less common, assertive predatory fish like Giant Snakeheads and Jaguar Cichlids intrigue advanced aquarists. Caution is required as both can become aggressive, especially towards smaller tank mates.

Native to tropical Asia, Giant Snakeheads command attention, growing over 3 feet long. They are voracious predators requiring large prey items like feeder fish. Despite their reputation, captive bred individuals can be tamed. They need a spacious tank and frequent water changes to thrive.

The aptly named Jaguar Cichlid is a stunningly colored fish from Central America. They are considerably smaller than Giant Snakeheads, reaching 14-16 inches as adults. But they are aggressive territorial fish, best kept with robust tankmates that won’t be bullied. Despite their care requirements, Jaguar Cichlids are immensely popular thanks to their beautiful black and yellow spotted patterning.

Goldfish and Tinfoil Barb

Even commonly kept fish like single-tailed Goldfish and Tinfoil Barbs reach impressive sizes in optimal aquarium conditions.

Single-tailed Goldfish are the iconic orange fish found in pet stores everywhere. When given spacious aquariums, goldfish continue to grow throughout their 10+ year lifespans, potentially exceeding 18 inches. Though demanding, keeping a giant Goldfish can be immensely rewarding for patient aquarists.

Tinfoil Barbs are mainstays of large community tanks thanks to their schooling behavior and flashy metallic sheen. Average lengths are 8-10 inches, but they can grow over a foot long in ideal conditions. Their powerful swimming makes them best for long tanks over 125 gallons.

Iridescent Shark and Oscar

Two of the most popular beginner monster fish are Iridescent Sharks and Oscars. Though manageable for dedicated aquarists, both can outgrow home aquariums if not rehomed responsibly.

Iridescent Sharks are not true sharks but a species of catfish. Juveniles exhibit a shark-like appearance and iridescent sheen that entices beginners. But they grow extremely fast, potentially exceeding 4 feet in tanks. Proper care and planning are critical with this fish.

Oscars are South American cichlids prized for their intelligence and charismatic personalities. They average 10-12 inches but can eclipse 15+ inches in large home aquariums. Oscars require pristine water conditions and plenty of space to thrive long-term.

Big Fish in Bedroom Aquariums

Many aquarists consider placing a large tank in their bedroom when envisioning a dream aquarium. But there are some important factors to consider before putting big fish in bedroom aquariums.

The Pros:

  • Enjoy your fish anytime – a bedroom tank allows you to relax and observe your aquatic pets before bed and when waking up.
  • Convenience – routine maintenance and feeding are simpler with a tank in the bedroom versus elsewhere in the home. No need to trek to the tank daily!
  • Immersive experience – a big bedroom aquarium can create a peaceful underwater scene to enhance relaxation and sleep. The soothing sounds of filters and bubblers promote tranquility.

The Cons:

  • Disrupted sleep – pumps, equipment noise and nocturnal fish activity can interfere with sleep quality for sensitive individuals. Lighting on timers also contributes.
  • Limited space – bedroom tanks are often narrower than deep, limiting options for large active swimmers. Weight limits on floors also restrict size possibilities.
  • Tank maintenance – while convenient day-to-day, bedroom tanks often require bucketing out water for partial water changes rather than using a Python. Saltwater tanks also raise humidity via open tops.

Overall, bedroom aquariums can work well for calm, unobtrusive fish provided noise and lighting are addressed properly. Narrow floor plans do limit tank dimensions so fish size must be chosen carefully.

Big Fish in Small Aquariums: A Feasible Idea?

Many aquarists new to the hobby often ask if large fish species can be permanently kept in relatively small aquariums compared to public exhibits. There are several factors to consider when evaluating the ethics and logistics of this idea.

Regarding ethics, fish growth can become stunted long-term in undersized tanks due to suppressed development and chronic stress. Nature cannot be replicated in small volumes of water. Providing big fish an adequately sized habitat should be the priority for any responsible aquarist.

That said, juvenile big fish can ethically be raised in small to medium tanks temporarily. The key is having a plan ready for future rehoming or upgrading to larger aquariums, sometimes hundreds or thousands of gallons. Attempting to stunt fish growth permanently should never be the goal.

Logistically, small tanks require more concentrated maintenance to maintain water quality. Filtration systems for big fish also often become a complex DIY project in small aquariums. And even if basic health can be sustained, small tanks fail to meet the behavioral needs of active species.

The Freshwater Giants: Big Fish for Large Aquariums

Truly monstrous freshwater fish require massive aquariums closer to public zoo exhibits than typical home setups. Some giants are only suited for experts with space, resources, and dedication.

Big Freshwater Fish

  • Arapaima – South America’s legendary air-breathing giants. Monster adults exceed 10 feet and 400 pounds.
  • Alligator Gar – Prehistoric giants from North America reaching 10 feet long and over 100 pounds.
  • Giant Stingray – Southeast Asian monsters with wingspans over 16 feet recorded in the wild. Can reach up to 600 pounds.
  • Mekong Giant Catfish – Critically endangered giants from Asia reaching 10 feet and over 700 pounds.
  • Beluga Sturgeon – Massive sturgeon species that can exceed 15 feet and 3000 pounds around the Caspian Sea.
  • Sawfish – Primitive giants with elongated saw-like snouts, reaching 18 feet. Require massive tanks.
  • Giant Gourami – Tropical species that can reach up to 28 inches long. Less massive but still require large tanks.

Large Peaceful Community Fish

  • Common Pleco – Iconic suckermouth catfish reaching up to 24 inches. Undemanding and peaceful.
  • Clown Knifefish – Electric knifefish growing over 15 inches. Shy but require length in a peaceful community.
  • Bala Shark – Streamlined giants reaching 14 inches. Excellent open swimmer. School in groups.
  • Clown Loach – Colorful eel-like fish growing 12+ inches. Social bottom dwellers.
  • Silver Dollar – Shiny metallic giants reaching 6-8 inches. Active schooling fish.
  • Freshwater Angelfish – Iconic cichlid reaching 6-12 inches. Peaceful but can be territorial.

Long Freshwater Fish for Aquariums

  • Arowana – Elegant predators with huge appetites. Grow 3 feet and require tank length.
  • Featherfin Knifefish – Graceful with undulating fins. Need minimum 4 foot long tanks.
  • Freshwater Moray Eel – Snake-like fish that can exceed 5 feet long. Reclusive predators.
  • Payara – Streamlined characins with vampire fangs. Attain lengths over 2 feet.
  • Reedfish – Eel-like fish that can grow to 3 feet. Secretive bottom dwellers.
  • Ropefish – scaleless predators with snake-like bodies exceeding 3 feet. Require length.

Aquarium Predators: Do Big Fish Eat Small Fish?

A common question surrounding big monster fish is whether they will consume smaller tank mates. There are a few key considerations when exploring the predatory instincts of large aquarium fish:

  • Species Matters – Predatory fish like Arowana and Alligator Gar will eat anything they can swallow. But large herbivores such as Common Plecos will not. Knowing the natural behaviors of the fish is critical.
  • Size Difference – Fish are opportunistic feeders. They will consume tank mates that are small enough to swallow whole. Bigger prey is more challenging.
  • Individual Personality – Some individual fish are more aggressive by nature than others, increasing chances of predatory behavior.
  • Environment Stressors – Overcrowding, inadequate space, poor water quality, or insufficient feeding can bring out predatory tendencies even in typically docile fish.
  • Hunger Levels – Well-fed predatory fish are less likely to hunt tankmates. Providing a varied carnivorous diet is key.

With careful selection of compatible species, adequate space, and proper feeding, large predatory fish and smaller tank mates can coexist peacefully in most home aquariums. Knowing the species’ natural tendencies is critical.

Legalities of Keeping Game Fish

While most aquarium monster fish are legal to keep with only a standard pet license, some “game fish” species are regulated by state laws. Two factors determine legality – native status and sport fishing regulations.

Is It Legal to Keep Native Game Fish?

Native sport species like Largemouth Bass and Alligator Gar cannot be collected from the wild for home aquariums in most regions. However, captive bred or legally imported individuals often can be owned with proper licensing. State regulations vary regarding live possession and breeding.

Transporting Native game fish across state lines or international borders is almost always illegal without explicit permits for conservation, education or research purposes. Even with licenses, stringent regulations apply to native sport fish.

Regulations for Exotic & Non-Native Game Fish

Introduced sport fish like Rainbow Trout or Peacock Bass generally have fewer ownership restrictions. Live transport remains regulated but acquisition itself is legal in most areas.

International exotics like Arapaima are only legally imported with licenses proving captive breeding. Commercial breeding allows ownership yet regulations on interstate transport persist. State laws also vary regarding which exotics are permitted. Proper research is imperative.

The Illusion Factor: Why Fish Appear Bigger in Aquariums

Why do massive fish like Arapaima seem even larger in home aquariums than public zoo exhibits? The answer lies in how our eyes interpret spatial relationships and relative scale. Here’s the science behind the captivating illusion that fish appear bigger in aquariums.

How Spatial Perception Plays a Role

Big fish have vast environments and small points of reference in natural habitats and public aquariums. This spatial relationship makes them appear proportional at large sizes.

In small home tanks, limited space and familiar decor like gravel and decorations provide an inherent sense of scale. Our spatial perception realizes the fish is exceptionally large relative to its environment.

The Impact of Optical Illusions

Optical illusions also contribute to the captivating effect. Refraction through glass distorts our perception of true sizes. And near the tank edges, fish appear magnified due to the convex curvature.

Foreground proximity also plays a role. Large fish swimming right up to the tank front appear immediacy larger than when resting in the backdrop. This forced perspective enhances the illusion of size.

What to Do When Your Fish Outgrows the Tank

So you’ve raised a baby monster fish and now realize it is too large for its current home aquarium – what should you do? Firstly, don’t panic! With some planning and preparation, you can ensure your oversized fish continues to thrive. Here are a few options to consider:

  • Upgrade Tank Size – If you have space and budget, upgrading to a larger tank suited for your fish’s adult size is ideal. This minimizes stress and change.
  • Rehome Responsibly – Finding a capable new owner with proper facilities is preferable over releasing into the wild. Use online forums and local fish stores to rehome responsibly.
  • Explore Public Display – Contact local aquariums and zoos to see if they will adopt. Some even allow private individuals to sponsor exhibit tanks.
  • Temporary Housing – For short term, plastic tubs or stock tanks can house fish until more permanent accommodations are arranged. Perform frequent water changes.
  • Divide Time in Existing Tank – Use tank dividers to give your fish some extra space while rotating time in the main tank. Helps bide time for an upgrade.

With some foresight and planning, monster fish that have simply outgrown their existing tanks can continue to thrive. Prioritize upgrades or responsible rehoming strategies.

The World’s Largest Fish Aquariums

Public aquariums allow people to observe monster fish that require gallons of water safely. Here are some of the record-breaking giants from around the world:

Largest Public Aquarium Fish Exhibits

  • Georgia Aquarium Ocean Voyager Exhibit – 6.3 million gallon tank housing Whale Sharks, Manta Rays and more marine megafauna.
  • Chimelong Ocean Kingdom Whale Shark Exhibit – 10 million gallon tank with the largest viewable population of Whale Sharks and countless other fish.
  • Shedd Aquarium Wild Reef Exhibit – Over 1 million gallon coral reef display featuring sharks, rays, and thousands of smaller reef fish.
  • Monterey Bay Aquarium Open Sea Exhibit – 1.2 million gallon tank with one of the first large scale views of pelagic ocean life.
  • Okinawa Churaumi Aquarium Kuroshio Tank – 7.5 million gallon tank housing multiple Whale Sharks, marine mammals, and oceanic predators.

Largest Home Aquariums

  • Red Sea REEFER – Commercially available 500 gallon reef aquarium for home use.
  • Neptune Systems Apex – Controller system capable of automating up to 20,000 gallons of home aquariums.
  • Acrylic custom builds – Custom aquarium builders create monsters up to 30,000 gallons for high-end clients. The largest recorded was over 53,000 gallons.

While public aquariums use giant tanks for educational conservation efforts, ambitious home aquarists also create monumental setups previously only seen in zoos. Home aquariums over 500 gallons are increasingly common for devoted fish keepers. And with custom builders and automation controllers, the possibilities in residential aquariums are nearly endless for those with the passion and resources to pull off epic home fish rooms.


From prehistoric Alligator Gars to the legendary giants of the Amazon, massive fish captivate the imaginations of aquarists unlike any others. This guide has provided an overview of the most popular big fish in home aquariums, from monster fish care and behavior to the innovations making large private aquariums possible.

Whether you currently keep fish or aspire to one day, the essential information covered in this guide provides a window into the awe-inspiring world of big fish in home aquariums. With the right mix of passion, responsibility and resources, any aquarist can safely keep a living giant.