Sand catfish

Where they come from

Sand catfish (Arius arenarius) are coastal catfish that hang around sandy, silty shorelines and estuaries. Think river mouths, mangrove edges, and those areas where fresh and salt mix and the bottom is basically a buffet of little critters.

That habitat tells you almost everything: they like moving, oxygen-rich water, they root around on the bottom, and they do best in brackish that is kept steady rather than fiddled with every week.

Setting up their tank

This is an advanced fish mostly because of size, waste, and long-term space. A cute juvenile turns into a serious, heavy-bodied catfish. Plan the adult tank from day one, not the "I'll upgrade later" plan (I have tried that plan - it gets stressful fast).

• Tank size: big footprint beats tall. Aim for 6 ft length as a starting point for a single adult, larger for multiples.
• Filtration: oversize it. Canister or sump, plus strong mechanical filtration for sand and leftovers.
• Flow and oxygen: add powerheads/wavemakers and keep surface agitation strong.
• Substrate: sand is your friend. They mouth the bottom and you want something smooth.
• Hiding spots: big PVC elbows, lengths of pipe, or rockwork that cannot collapse. Keep it stable and heavy.
• Lighting: they do not need it bright. Dimmer setups keep them calmer.

For brackish, I keep it simple: marine salt mix, a refractometer, and small adjustments. Most hobbyists land somewhere around low to mid brackish for this kind of catfish, but the bigger deal is consistency. Pick a target salinity and keep it there rather than bouncing around.

Water quality matters a lot because they are messy eaters and thick-bodied fish that can outgrow your filter. Expect higher nitrates if you slack off. Big, regular water changes and a prefilter sponge you rinse often will save you headaches.

What to feed them

They are bottom-feeding predators and scavengers. In captivity they learn schedules fast. Mine would be waiting at the front like a dog the moment the room light came on.

• Staples: sinking carnivore pellets or wafers made for large catfish/predators.
• Meaty foods: shrimp, mussel, clam, squid, fish flesh (use clean sources), and earthworms.
• Frozen: krill, chopped prawn, and mixed marine blends work well.
• Occasional treats: live foods like ghost shrimp can get picky individuals eating again.

Feed smaller fish more often, and big adults less often. Overfeeding is the fastest way to sour the tank. I like to feed at dusk and then do a quick "leftover patrol" 10-15 minutes later with tongs or a net.

How they behave and who they get along with

Sand catfish are generally not "mean" fish, but they are absolutely predatory and they get big. If it fits in the mouth, it is food. If it does not fit, it is usually ignored... until feeding time gets competitive.

They are mostly bottom-oriented and like to cruise, wedge into caves, and patrol the tank after dark. Some individuals are bold and out in the open, others turn into living logs under a pipe all day. Both can be normal.

• Good tankmates: robust brackish fish that are too large to swallow and can handle the same salinity (big scats, monos, larger brackish puffers with caution, sturdy archerfish in roomy setups).
• Avoid: anything small (will be eaten), delicate finned fish, and bottom dwellers that compete for the same caves (smaller catfish, gobies, loaches).
• Group vs single: juveniles may tolerate company, but adults often do best singly unless you have a very large system with lots of space and multiple hides.

Breeding tips

Realistically, breeding Sand catfish in home aquariums is uncommon. Many Ariidae catfish have unusual breeding behaviors (including mouthbrooding in some species), but getting the triggers right in a closed system is tough, and you would need a very large, stable brackish setup and a compatible pair.

If you ever want to take a swing at it, think seasonality: heavier feeding during a "wet season" phase, then a shift in water conditions that mimics coastal changes (temperature and salinity nudges, not swings), plus a huge amount of space and hiding areas. Even then, do not be surprised if nothing happens. Most hobbyists keep them for their personality and presence, not as a breeding project.

Common problems to watch for

• Barbel erosion and mouth damage: usually from sharp substrate, dirty bottoms, or bacterial issues. Sand, strong filtration, and not letting food rot helps.
• Bloat/constipation: often from overfeeding or too much rich food. Mix pellets with leaner seafood, feed less, and keep temps steady.
• Ich and other parasites: can show up after new fish. Quarantine new arrivals and do not assume brackish automatically prevents disease.
• Ammonia/nitrite spikes: these fish can overwhelm a new or undersized biofilter quickly. Cycle fully and upgrade filtration early.
• Aggression at feeding time: not always constant fighting, but sudden lunges and fin damage can happen in mixed predator tanks.
• Salinity mismatch stress: drifting salinity from top-offs or sloppy measuring can make them sulk, stop eating, or breathe hard.

The biggest "problem" I see with these is people underestimating the adult size and waste output. If you build the system around the adult fish - big footprint, heavy filtration, steady brackish, and a sand bottom - they are actually pretty straightforward day to day.