Naturally, common sense tells us that the needs of a fish will be proportional to its size. Therefore the needs of a 1-inch Cardinal Tetra are miniscule compared to the needs of an Arapaima which is over a hundred times bigger than the Cardinal Tetra. This should make sense, right?

The purpose of this article is to highlight this fact; moreover, it is to present the not-so-obvious realties in keeping monster fish. After all, with some fishkeepers, common sense is not too common (see my December 2015 column) and in fact, may be a rarity for some.

The Big Fish

Before we proceed with this article, let us agree as to what a monster fish is. Since “big” is a relative term that can vary from person to person, let us agree that a monster fish is any fish that grows to a maximum size of at least 18 inches or a foot and a half. Let us just say anything less than 18 inches is big, but anything more than 18 inches is a certified monster fish. At least, with 18 inches as our standard, we have quantified the size of a fish we shall qualify as a monster fish. Going Big My first experience with monster fish was in the late 1970s or early 1980s. You could say that about the same time that monster fishkeeping became a thrilling hobby, Michael Jackson was also hitting it big with his song “Thriller.”

Back then, the Filipino fishkeeper was introduced to highly desirable monster fish like the Red Tailed Catfish, Tiger Shovelnose Catfish, Red Pacu, Paroon Shark, Giant Snakehead, Silver Arowana, Australian Arowana, Asian Arowanas, Alligator Gars, and the monster of them all, the Arapaima. Filipino fishkeepers for the most part had never seen these fish before. This was probably was the first time that we experienced fish that grew larger than our aquariums. The more popular term back then was “Tank Busters,” derived from the popular book with the same title by Mary E. Sweeney.

This era was mind-blowing…but so much more exciting. By the mid-1990s, interest in fishkeeping in general slowed down until a rebirth of the industry was brought about by the introduction of the Flower Horn. By the turn of the century, fishkeeping was on an uptrend, and monster fishkeeping in the Philippines has been on an upswing ever since.

Big Communities

In monster fishkeeping, size does matter. Yes, it is all about size. Some are big; some are much bigger; and others are just humongous. Thus it is important that fish of similar sizes are kept together. If you have different species of monster fish in a grow-out tank that measure from 6 to 10 inches each, you may have relative success in keeping them together.

But further size differences among tank inhabitants will be a problem. While size discrepancy among occupants of a tank is important, you will also have to determine their potential maximum size in captivity. Otherwise, some might be left behind and one day become dinner for some giant tank residents. In the world of the monster fish, small ones are food and not friends. In determining which species you may keep together in one tank, research plays an important role.

Find out what maximum size they can potentially attain in captivity. Personally, I have the one-meter rule. Any monster fish with a maximum size between 18 inches (or about 60 cm) to 1 meter (100 cm or about 39 inches) may be considered a “small” monster fish. Popular examples of these are Peacock Basses from the genus Cichla, some rays like the Potamotrygon motoro, Arowanas, wolf fish like Hoplias malabaricus and H curupira, some species of Bichirs from the genus Polypterus, Asian Tigerfish from the genus Datnioides, most gars, some catfish like the Tigrinus Catfish, Lima Shovelnose Catfish, Marbled Catfish, and so on.

The list goes on for quite a bit. Those with a maximum size of 1 meter and more are the “large” monster fish. These are the big boys and most likely will be too big for a regular aquarium. The more popular examples are catfish like the Red Tail Catfish, Tiger Shovelnose Catfish, and Ripsaw Catfish; the Paroon Shark; Pacus like the common Red Pacu or the rare Black Pacu; the Alligator Gar; snakeheads like the Giant Snakehead, Bull’s-Eye Snakehead, and the rare Northern Snakehead; the highly desirable Payara (Hydrolycus armatus) and the Goliath Tigerfish (Hydrocynus goliath), and of course, the Arapaima. Mixing “small” monster fish with “large” monster fish may be a potential disaster in the long term.

However, if you have many large tanks, you may just keep monster fish of similar sizes in one tank and just keep on transferring the bigger ones to more appropriately sized tanks once they get to be a headache. The Tank’s the Thing Obviously, to be able to keep monster fish, you will need monster-sized tanks. I always thought that a 75-gallon tank measuring 48’ (inches, length) x 18’ (width) x 20’ (height) was a large tank. For the regular fishkeeper, this is indeed true. But for the monster fishkeeper, this is way below standard. Personally, I say that a 180-gallon tank measuring 72’ x 24’ x 24’ should be the smallest tank that can qualify for keeping monster fish.

The large monster fish, technically, will have to be moved out of this small tank someday. Nowadays, aquariums are larger. The largest all-glass aquarium I heard of in the Philippines measures 16” (feet) x 5” x 4”. If my calculations are correct, this is a staggering 2,400-gallon tank. Monstrous Filters With monster-sized tanks come monster-sized filters. To be able to filter a tank containing a huge volume of water, you will require a filter that has a big capacity with a pump able to provide a sufficient flow rate. I will not discuss what filter to use since there are endless possibilities as to which kind to use; nor will I discuss what filter media to use as there are so many kinds which result in the same biological processes. I will simply look at the two aspects mentioned: capacity and flow rate.

Filter capacity is the physical size or volume of the filter. My rule of thumb for filter capacity is a minimum of 20% of the total water volume of the tank. That means my filter chamber filled with filter media should be at 1:5 ratio of my tank. If my tank is 300 gallons, then my filter capacity should be at least 60 gallons. If the 2,400-gallon tank were mine, I would design a filter that can hold at least 480 gallons. To give you an idea how enormous this project is, a monster-sized tank measuring 8” x 3” x 2.5” is only 450 gallons. Even if I used this as a filter, I would still be short by 30 gallons of my objectives. As for flow rate or the rate of water displacement, the optimum rate should be 4 times rotation in a given hour. This means if you have a 300-gallon tank, a pump that can handle 1,200 gallons per hour should give you optimum flow rate. In our ultimate 2,400-gallon tank project, we will need a pump that can displace 9,600 gallons per hour, or install 4 sets of pumps which, when combined, can process 2,400 gallons per hour.

Thickness Matters

By the way, in customizing these tanks, make sure that the glass thickness is appropriate. Monster fish are highly capable of breaking aquariums, especially if the glass thickness is 10 millimeters (mm) or less. A more viable option is to have aquaponds (one side glass and four sides concrete) or ponds. This way they can be built big and sturdy. But whatever you decide to get—whether an all-glass aquarium, an aquapond, or a pond—the bigger it is, the better and more enjoyable monster fishkeeping will be.

Forget about the thin and flimsy glass covers that go with your purchase of a standard commercially available tank. They can easily break those with a simple jump and you will find your dear fish dried up on the floor. You have to use 8 to 10 mm thick glass just to cover your tanks. Monster fish can also knock things around in the aquarium when they swim. They can easily dislodge pipes, hoses, pumps, driftwood, and rocks: basically, anything inside the tank. Thus, these things should be secured very well so they do not dislodge or break something inside the tank.

I have a 28-inch Fire Eel with a girth of about 10 inches; when he swims, he easily moves the huge driftwood I had difficulty putting inside the tank. That driftwood, which probably weighs 5 kilos, is always dragged around the tank when he swims. Giant AppetitesAnother very important fact to consider is that monster fish attain their huge size because they have big appetites. These guys simply eat a lot, and the fishkeeper must have the commitment to feed them correctly. Forget typical aquarium fish feeding. If you buy pellet food by the can, think about buying commercially available fish food by the sack. Think big!

While they are small, feeding them guppies and small feeder goldfish is a good starting point, but once your monster fish attain their ideal size, look in the freezer, look for your dinner sized fish, and offer these to them. These guys eat more than you do. Manila Ocean Park once had a 27-inch Indo Tigerfish, it was easily the biggest Indo Tigerfish I ever saw; it was about the size of a standard 35-gallon tank. It ate two pieces of fish of the size that could feed a family of 4—and it ate twice a day! Just imagine how much fish an 8-foot Arapaima will consume. Monster fish may eat a lot, but feeding time is sure to be a frenzy all fishkeepers and many who are curious about the hobby will enjoy watching.

Monstrous Maintenance

Given how it eats, tank maintenance will be a huge job for the monster fishkeeper. You may even work harder cleaning your tank on weekends than you do at work in the office on weekdays. A monster fish creates so much bioload that you will have to support the filter system with regular water changes. The amount of water you will need for every water chance is tremendous. Just do the math. A 30% water change for a 50-gallon tank is a mere 15 gallons.

Proportionately, a 30% water change for a 300-gallon tank is 90 gallons. In our dream 2,400-gallon tank, a 30% water change is 720 gallons. That is enough water for your garden and all the neighborhood plants! Filling up your monster-sized tanks will also take some time. You may see your weekend slip away before you are able to fill it up. You may also need special tools for cleaning your tank. Forget about commercially available gravel cleaners, sponges, and hand brushes to scrape tough algae. Go big and adapt your tools; think of using one inch thick hoses for siphoning tank water, foam filter mats for wiping the glass, and floor brushes with long handles to reach the deep ends.

The Last Consideration

Your investment costs will naturally be on the high side. Monster fish are generally more expensive (except for some cheap ones like the Red Tail Catfish, Tiger Shovelnose, Paroon Sharks, etc.). Monster-sized tanks may cost as much as a car. Your filter systems will require a bigger budget. Their monthly food costs may be equal to that of a family of three. Your electricity and water bill will surely be more expensive than what you’ll spend keeping a studio unit in a condominium. Your expenses in keeping monster fish will be a sizeable investment. But then again it is all worth it if monster fish is your passion.

The pride and joy you will take in having a fish bigger than you is the envy of all fishkeepers. This separates the men from the boys. Who wouldn’t want to have the Manila Ocean Park as your own fish room? Monster fish keeping is not for everyone but if you are one of the few who are able to keep your own collection, always bear in mind that everything in monster fishkeeping is a monstrosity.


This appeared in Animal Scene’s January 2016 issue.