Freshwater shark

Where they come from

Wallago attu is a big predatory catfish from South and Southeast Asia - think river systems like the Indus, Ganges, and parts of Myanmar and Thailand. People call it a "freshwater shark" because of the long, torpedo body and the way it hunts in open water, but its attitude is pure catfish.

In the wild it deals with seasonal changes, murky water, and strong current. That background matters because this fish is built for space, oxygen, and eating other fish.

Setting up their tank

I will be blunt: this is not a "big aquarium" fish, it is a "private pond or indoor pool" fish once it grows. Juveniles can be started in a very large tank for a while, but they outgrow normal home setups fast.

They are powerful swimmers and they spook hard. Give them long straight runs, rounded corners if you can, and keep the layout simple so they do not smash themselves on decor during a nighttime bolt.

• Footprint first: long and wide beats tall. Open swimming room matters more than depth.
• Filtration: think pond-level turnover and bio capacity. Big sump, big prefilter, easy access for cleaning.
• Flow and oxygen: strong surface movement and plenty of dissolved oxygen. They sulk in stale water.
• Substrate and decor: sand or bare bottom is easiest. If you use wood/rocks, keep them smooth and pinned down.
• Lid: tight and heavy. They can surge upward and launch when startled.

For water parameters, do not obsess over a magic number. Stable, clean freshwater wins. I have had the best results keeping nitrates low with big water changes and over-filtering rather than chasing pH. Warm tropical temps are fine, just keep oxygen high because warmer water holds less.

What to feed them

Wallago attu is a predator with a serious gape. Juveniles will take meaty foods right away, and adults will happily eat fish, shrimp, and chunks of anything that smells like protein.

• Staples: white fish fillet, shrimp, prawns, mussel, squid (not every day), earthworms
• Convenient options: quality carnivore pellets once they accept them, frozen silversides or similar
• Treats: live foods like earthworms or feeder shrimp from a safe source

Do not overdo oily foods or mammal meat. Beef heart and chicken are popular in some circles, but I have seen big predators get fatty and sluggish on that stuff. Better to rotate seafood and fish-based foods and keep portions sensible.

Feeding rhythm: smaller fish can eat more often, but adults do better with larger meals a few times a week. If the belly stays rounded for days, you are feeding too heavy.

How they behave and who they get along with

They are not community fish. Even if yours seems calm, it is a sit-and-wait hunter that can flip the switch fast. Anything that fits in the mouth is food, and a lot more fits than you think.

• Temperament: predatory, can be skittish, can be surprisingly bold at feeding time
• Activity: often more active at dusk/night, but they learn your schedule
• Tankmate rule: if you are asking "will it eat this?" the answer is probably yes

If you insist on tankmates, you are looking at very large, robust fish that cannot be swallowed and will not harass it. Even then, you are rolling the dice, and the tank has to be huge so everyone has room to get away. A stressed Wallago can panic and injure itself, and a crowded tank makes that more likely.

Breeding tips

Breeding Wallago attu in home aquariums is basically a non-event. They are big, seasonal river spawners, and most successful breeding is done in ponds or commercial settings where you can mimic monsoon cues or use hormones.

If you ever end up with a mature pair in a pond, the rough idea is heavy feeding leading into large water changes and a rainy-season style shift (slightly cooler water and big fresh water influx). But in a typical glass tank setup, it is not something to count on.

Common problems to watch for

• Injury from spooking: scraped snout, torn fins, broken whiskers from hitting decor or lids
• Water quality crashes: big predators make big waste, and they go downhill fast if filtration or maintenance slips
• Bloat/constipation: from overfeeding, too much oily food, or not enough variety
• Parasites from live feeders: especially if you use store feeders or outdoor-caught fish
• Aggression accidents: tankmates disappearing overnight or sudden bullying in tight quarters

Quarantine anything you plan to feed or add as a tankmate. With a fish this valuable (and this messy to medicate in a giant system), prevention is way easier than trying to treat an outbreak after the fact.