Day's catfish

Where they come from

Day's catfish (Nedystoma dayi) is one of those South Asian river catfish that looks "plain" in photos, then turns into a seriously impressive fish once it settles in and starts cruising at night. They come from warm, moving waters where the bottom is sand, silt, leaf litter, and scattered rocks.

Think rivers and floodplain channels that change with the seasons. That background matters, because this fish tends to do best in a tank that feels like a riverbank, not a bright planted community setup.

Setting up their tank

This is an advanced fish mostly because of size, strength, and mess. They are built like a torpedo and they eat like one too. Give them space to turn, a bottom they can sift, and filtration that can handle big meals.

• Tank size: bigger than you think. I would not bother under 5 ft length, and 6 ft is where it starts feeling comfortable.
• Footprint matters more than height. They use the bottom and midwater, especially after lights out.
• Substrate: sand is my pick. Fine sand lets them root around without wearing down their barbels.
• Hardscape: rounded rocks, driftwood, and a couple of solid caves. They like having a "home base" to wedge into.
• Flow and oxygen: moderate to strong flow plus lots of surface agitation. These fish act way more confident in well-oxygenated water.
• Lighting: keep it subdued. Floating plants or dim LEDs make them show themselves more.

For water numbers, aim for the warm side of tropical freshwater and keep things steady. I have had the best luck with mid-70s to low-80s F and neutral-ish pH. The exact number matters less than stability and clean water.

What to feed them

They are predators and scavengers. In my tanks they learn routines fast, and they will come out for food once they feel safe. The trick is giving them meaty foods without turning the tank into a nutrient soup.

• Staples: sinking carnivore pellets and quality catfish sticks (something that holds together and does not cloud instantly).
• Frozen: prawns/shrimp, fish fillet, mussel, krill, bloodworms for smaller individuals.
• Live (optional): earthworms are a great conditioning food and usually accepted immediately.

Feeding schedule: I like a smaller meal most evenings rather than massive dumps of food. If you want a good rhythm, feed after lights go down and keep an eye on leftovers the next morning. If food is still sitting there, you fed too much.

How they behave and who they get along with

Day's catfish is mostly a nighttime bruiser. Not a mindless killer, but absolutely a "if it fits, it disappears" fish. They spend the day tucked under wood or in a cave, then patrol once the room gets quiet.

• Temperament: assertive predator, not a delicate community catfish.
• Activity: crepuscular/nocturnal. Expect more action at dusk and after dark.
• Territory: they will claim a favorite hide. More hides = fewer issues.

Tankmates need to be big enough to not be viewed as food and sturdy enough to handle a bit of chaos at feeding time. I have had the best luck with medium-large, confident fish that occupy midwater and do not sleep on the bottom.

Also keep in mind they can be grabby about food. If you keep slower tankmates, you will end up target-feeding the catfish or the others will get outcompeted.

Breeding tips

Realistically, breeding Nedystoma dayi in a home aquarium is not something you see often. Most fish in the hobby are wild-caught, and spawning likely ties into seasonal changes (big water changes, temperature shifts, and heavy feeding) plus space.

If you want to try anyway, the best "hobbyist approach" is to keep a well-fed group in a very large tank, give them lots of cover, and simulate a rainy season with larger, cooler water changes and increased flow. Just know that even if they spawn, raising fry from a big predatory catfish is a whole project on its own.

Common problems to watch for

Most issues I have seen with these come down to three things: stress from a too-bright/too-busy setup, poor water from heavy feeding, and injuries from rough decor or bad netting.

• Barbel wear: usually from sharp gravel or filthy substrate. Switch to sand and step up maintenance.
• Mouth and snout damage: they can spook and slam into glass or rocks. Keep hardscape smooth and give them shaded cover.
• Bloating/constipation: common if you feed lots of dry foods without variety. Mix in shrimp, worms, and smaller meals.
• Ich and skin issues after import: wild fish can arrive stressed. Quarantine, keep oxygen high, and avoid sudden parameter swings.
• Filter clogs and nitrate creep: big meaty foods create a lot of waste. Expect to clean filters and do meaningful water changes.

If your fish never comes out and seems "invisible" for weeks, that is usually the tank telling you something. Dimming the lights, adding a proper cave, and reducing daytime commotion often flips the switch. Once they feel secure, they get bold fast.