Saul's whale catfish

Where they come from

Saul's whale catfish (Denticetopsis sauli) is one of those oddball South American cats that shows up in the hobby rarely, and usually without much fanfare. Most of the ones I've seen in the trade trace back to blackwater and clearwater tributaries in the Amazon/Orinoco region (depending on the collection chain), where the water is soft, warm, and the fish spend a lot of time tucked into leaf litter and root tangles.

They look kind of plain at first glance, but they're fascinating once you realize how much of their life happens in the shadows. Think "leaf litter ambusher" more than "glass surfer."

Setting up their tank

If you try to keep this species like a typical community catfish, you'll be frustrated and the fish will be stressed. They settle in best when you build the tank around cover and low-key lighting, then let them come out on their own schedule.

• Tank size: I'd start around 20-30 gallons for a small group, bigger if you want calmer behavior and steadier water.
• Substrate: fine sand is your friend. They like to nose around, and rough gravel can beat up their barbels.
• Cover: piles of leaf litter (catappa/oak/beech), driftwood, and tight caves. I like using chunks of branchy wood so they can wedge themselves in.
• Lighting: dim. Floating plants or tannins help a lot.
• Flow: moderate and well-oxygenated, but no jet blasting their hiding spots.
• Filtration: strong bio filtration and clean water, but keep intake prefilters on - these fish can be surprisingly good at getting into trouble.

Water-wise, I keep them warm (mid 70s to low 80s F), soft to moderately soft, and on the slightly acidic side if possible. More than chasing a magic number, focus on stability and cleanliness. Big swings in temperature or conductivity are where things go sideways fast.

What to feed them

They are predators/micro-predators. If you're hoping they'll live on flakes and the occasional algae wafer, you're going to end up with a skinny, hidden fish.

• Staples: sinking meaty foods like quality carnivore pellets, catfish tablets with high protein, and frozen foods.
• Frozen: bloodworms, blackworms, brine shrimp, mysis, chopped krill, and prawn/shrimp bits.
• Live (optional): blackworms are like a cheat code for getting new arrivals eating. Use clean sources.
• Feeding time: after lights out or at least at dusk. They feed way more confidently then.

A new Denticetopsis that won't eat in front of you isn't always "not eating." Watch the belly line over a couple weeks. If it's pinched in, step up the live/frozen and feed later at night.

How they behave and who they get along with

They're secretive, mostly nocturnal, and a bit twitchy in bright tanks. In a dim, leaf-litter setup, they calm down and you start seeing their real personality: slow cruising, sudden darting strikes, and lots of lurking under cover.

Compatibility is where people get burned. They are not mean in the "chase and bully" sense, but they are absolutely willing to eat anything that fits in their mouth.

• Good tankmates: calm midwater fish too big to swallow (larger tetras, hatchetfish that stay up top, peaceful cichlids that aren't fin-nippy), and other non-aggressive bottom fish that won't outcompete them.
• Avoid: tiny nano fish (they become food), aggressive cichlids, fin nippers, and super boisterous feeders that will starve them out.
• With their own kind: they can be kept in small groups if you provide lots of separate hides and break up line-of-sight. Crowding them into one cave invites stress.

I also recommend a tight lid. They can spook and bolt, especially right after a water change or if the room lights flip on suddenly.

Breeding tips

Real talk: breeding Denticetopsis sauli in home tanks is uncommon. Most hobbyists (myself included) end up focusing on long-term maintenance rather than expecting fry. That said, you can set the stage for it, and sometimes the fish surprise you.

• Keep a group: breeding is a lot more likely if you have multiple individuals and let them sort themselves out.
• Seasonal cues: slightly cooler, softer water changes followed by warming back up has been a trigger for a lot of South American cats. Think "rainy season" simulation.
• Spawning sites: tight caves, wood tangles, and thick leaf piles. Give them options at different depths.
• Food: heavy conditioning with live/frozen foods for a few weeks before you play with water change cues.

If eggs or fry do show up, the usual issues are predation (by tankmates or other cats) and filtration intakes. A separate, species-focused breeding tank with sponge filtration is the safer route if you're serious about trying.

Common problems to watch for

Most problems with this species boil down to three things: stress from bright/open tanks, starvation from competition, and water quality slipping in a tank that's fed heavy.

• Refusing food: often timing and shyness, not "mystery illness." Feed later, dim the tank, and try live blackworms to kickstart appetite.
• Barbel erosion: usually rough substrate, dirty substrate, or both. Switch to sand and vacuum gently around food areas.
• Skin issues and rapid breathing: frequently linked to poor oxygenation or dirty water. Add surface agitation and check your maintenance routine.
• Sudden hiding and flashing after water changes: temperature/pH/TDS swing. Match new water more closely and slow down the refill.
• Internal parasites (thin despite eating): not rare in wild-caught fish. Quarantine and consider a measured deworming protocol if weight won't stick.

If you give them a mature, dim tank with lots of cover and you feed like they actually eat in the wild, they turn from "invisible import" into a really rewarding oddball catfish. Just be ready to meet them on their terms.