Butter Catfish (Ompok bimaculatus)

What is a Butter Catfish?

The Butter Catfish (Ompok bimaculatus) is a large, sleek predatory catfish from the rivers and floodplains of South and Southeast Asia. It belongs to the family Siluridae — the same family as the European wels catfish — and shares that group’s hallmark scaleless, elongated body and long, rippling anal fin. In good aquarium lighting the fish has a faint glass-catfish quality: the flanks are silver-grey and semi-translucent, and the musculature is just visible beneath the skin. The easiest identification feature is the pair of dark spots sitting just behind the gill cover, the trait encoded in the species name bimaculatus (“two-spotted”).

Wild specimens reach 45 cm (18 in), though aquarium individuals typically settle around 25–35 cm (10–14 in) with adequate space and nutrition. The Butter Catfish is a mid-water cruiser rather than a bottom-hugger, often hovering in a characteristic head-slightly-down posture at rest. It is calm toward comparably sized or larger tank-mates, but an ambush predator toward anything small enough to fit in its gape — a fact that shapes every compatibility decision you make with this fish.

Where does the Butter Catfish come from in the wild?

The species ranges widely across South and Southeast Asia: India, Bangladesh, Sri Lanka, Nepal, Myanmar and Thailand, in habitats ranging from large lowland rivers and oxbow lakes to irrigation canals and seasonally flooded rice paddies. The water is typically warm, soft to moderately hard, and often turbid. Submerged wood, reed beds and dense marginal vegetation provide daytime cover.

The monsoon flooding cycle is significant: populations disperse into inundated fields each wet season, then retreat to river channels as waters recede. That flexibility explains the species’ tolerance of a fairly wide hardness range (4–18 dGH) in captivity. Most aquarium specimens are wild-caught juveniles from India or Southeast Asia, so quarantine new arrivals carefully.

What tank size and setup does the Butter Catfish need?

With a potential adult length of 45 cm (18 in), this is unambiguously a large-tank species. The minimum is 680 L (180 gal), and that figure assumes the fish reaches full size — which it will given time and good conditions. A long, low footprint suits it better than a tall column tank; aim for at least 180 cm (72 in) of front-to-back swimming length.

Substrate can be fine sand or smooth gravel. Although primarily a mid-water species, the Butter Catfish rests on the bottom occasionally; a soft substrate prevents skin abrasion. Provide large driftwood pieces, smooth rock caves or PVC pipe sections as daytime retreats — the fish is crepuscular and shelters for most of the day. Filtration must be robust: target 8–10× tank volume per hour across multiple filters, but keep return flow moderate rather than turbulent, as this species favours slow to gently flowing water.

What water parameters does the Butter Catfish need?

• Temperature: 24–28 °C (75–82 °F)
• pH: 6.5–7.5
• Hardness: 4–18 dGH

These parameters reflect the warm, lowland river and floodplain habitat across the species’ range. The relatively wide hardness tolerance makes it adaptable to most municipal tap water across its acceptable pH band. Ammonia and nitrite must remain at zero; for a fish this size, nitrate should be kept below 30 ppm with regular large water changes. Temperature stability matters — avoid swings of more than 1–2 °C between water changes. A quality heater with a reliable thermostat is essential.

What does the Butter Catfish eat?

Ompok bimaculatus is a carnivore and an opportunistic predator in the wild, feeding on smaller fish, crustaceans, aquatic insects and other invertebrates. In the aquarium, the diet should reflect that: large sinking pellets or sticks formulated for predatory catfish form a workable staple, supplemented with meaty foods such as whole prawns, mussel, earthworms, silversides and large bloodworms. Pre-killed or thawed frozen items are preferable to live feeder fish, which carry disease risk.

Feed once daily in the evening as the lights dim, since this species is most active at dusk and overnight. Remove uneaten food after a couple of hours to protect water quality. Juveniles will readily take small pellets and chopped foods; transition to larger, whole prey items as the fish grows.

How does the Butter Catfish behave, and what fish can live with it?

The Butter Catfish is rated semi-aggressive — a label that specifically reflects its predatory relationship with smaller fish rather than any general belligerence. Toward tank-mates that exceed its gape it is typically calm and even somewhat shy, retreating to its chosen cave during daylight. Specimens can be kept singly, and most aquarists keep just one per tank given the space requirements.

The critical compatibility rule is simple: any fish small enough to fit in the Butter Catfish’s mouth is a potential meal, and eventually will be. Suitable companions include large barbs (e.g. tinfoil barbs, large spanner barbs), substantial cyprinids, similarly sized Asian catfish such as Hemibagrus or Mystus species, large gouramis and robust cichlids of comparable body size. Avoid tetras, small rasboras, danios, small corydoras, shrimp and any nano fish.

For a full filterable list of compatible species, see Butter Catfish tank mates.

How do you tell male and female Butter Catfish apart?

Sexual dimorphism is subtle outside of breeding condition. Females become noticeably fuller-bodied when gravid, with a distinctly rounded belly that makes them appear considerably broader than males when viewed from above. Males are slimmer overall, with a slightly more elongated body profile. In juveniles and non-breeding adults the difference is modest and difficult to judge without a direct comparison of multiple individuals. Reliable sexing generally requires raising a group of fish to maturity.

Can the Butter Catfish be bred in captivity?

Breeding Ompok bimaculatus in the home aquarium is rated hard and has rarely been achieved by hobbyists. Commercial aquaculture in South Asia relies on hormonal induction. In nature, spawning follows monsoon cues — rising water levels, increased flow, cooler rainfall water and changing photoperiod — all of which are difficult to replicate at home.

A serious attempt needs a large dedicated breeding tank, a well-conditioned pair (identified by the body-depth difference above), and a gradual seasonal simulation: cooler water changes, increased flow, extended dimming of lights. The fish reportedly scatter adhesive eggs. Fry-rearing would require appropriately sized live foods. Most aquarists keep this species for its presence rather than any breeding ambition.

What diseases are common in the Butter Catfish?

As a scaleless catfish, Ompok bimaculatus is more susceptible to external parasites and medication toxicity than scaled species. Ich (Ichthyophthirius multifiliis) can establish quickly on the smooth skin; columnaris and bacterial infections can follow any physical damage. Skin flukes are a real risk in wild-caught individuals, so a four-to-six-week quarantine in a bare-bottom tank is strongly recommended before introducing any new arrival to a display tank.

Prevention is straightforward: excellent water quality, stable temperature and a varied diet eliminate most disease risk. Never apply medications, salt or chemical treatments at standard doses for scaled fish — reduce doses substantially and watch for distress.

Health note: medication dosing and disease diagnosis are beyond the scope of a care profile. For a sick fish, confirm the diagnosis against a reputable veterinary or aquatic-health source before treating, and factor in this species’ heightened sensitivity to chemicals as a scaleless catfish.

How long does the Butter Catfish live?

In a well-maintained aquarium, Ompok bimaculatus can be expected to live 5–10 years. The range reflects the difference between marginal conditions and optimal space, diet and water quality. Aquaculture data from South Asia supports robust longevity when nutritional needs are consistently met. Given the investment a tank of this size demands, a well-kept specimen is a long-term commitment and a genuinely impressive centrepiece for a large predator setup.