Hoplo Catfish (Hoplosternum thoracatum) — Species Overview
The Hoplo Catfish, known scientifically as Hoplosternum thoracatum (Valenciennes, 1840), is one of the most fascinating armoured catfish in the hobby. A member of the family Callichthyidae, it stands out not only for its robust, plated body but also for a remarkable physiological trait: the ability to breathe atmospheric air through a specialised intestinal respiratory organ. In my years of fishkeeping experience, this species has consistently proven to be both rewarding and surprisingly engaging to observe.
Native to tropical South America — including the Amazon and Orinoco basins, the Paraguay river system, and the islands of Trinidad and Tobago — Hoplosternum thoracatum inhabits shallow, warm, oxygen-depleted waters such as swamps, flooded rice fields, and seasonally inundated areas. This habitat has driven the evolution of its unique breathing adaptation.
In the aquarium, the Hoplo Catfish typically reaches 15–18 cm in length. Its coloration ranges from light brown to greyish-olive, often decorated with scattered dark spots or speckling. Like all callichthyids, the body is protected by two rows of bony plates. Sexual dimorphism is evident: males are slimmer, and their pectoral fin spines are notably thicker, often taking on an orange hue during the breeding season. Sexual maturity is reached at approximately 18 months of age.
Keeping Hoplosternum thoracatum: Tank Setup and Care
The Hoplo Catfish is an excellent choice for both beginners and experienced aquarists, thanks to its hardiness and peaceful temperament.
Tank size and water parameters. A group of 3–5 individuals requires a minimum tank of 80–100 litres. The species prefers the bottom zone, constantly sifting through substrate in search of food. It periodically rises to the surface to gulp air — a completely normal behaviour linked to its intestinal breathing organ. Unlike labyrinth fish such as the Siamese Fighting Fish or Blue Gourami, which use a specialised labyrinth organ above the gills, the Hoplo absorbs oxygen through the highly vascularised walls of its intestine. The tank lid must be kept closed but must allow a gap for air access.
Substrate and décor. Fine sand or smooth small gravel is ideal, as sharp substrates can damage the fish’s sensitive barbels and abdomen. Provide plenty of hiding spots — driftwood, caves, PVC pipes, or ceramic tubes. Note that this species is an enthusiastic digger and may uproot plants; potted plants or species with robust root systems (such as Echinodorus or Cryptocoryne) are recommended.
Compatibility. Hoplosternum thoracatum is entirely peaceful and poses no threat to any tank mates, including fish much smaller than itself. Ideal companions include Neon Tetras, Guppies, calm cichlids, and other bottom dwellers. Avoid housing with large, aggressive species that may harass or injure the catfish.
Care Parameters Table
| Parameter | Value |
|---|---|
| Tank Volume | from 80 L |
| Water Temperature | 22–28 °C |
| pH | 6.0–7.5 |
| Hardness (dGH) | 5–20° |
| Lighting | moderate |
| Flow | gentle to moderate |
| Substrate | fine sand or smooth gravel |
| Minimum Group | 2–3 individuals |
| Body Length (aquarium) | up to 18 cm |
| Lifespan | 8–10 years |
Feeding. The Hoplo Catfish is an omnivorous bottom feeder and an excellent aquarium janitor, consuming leftover food that reaches the substrate. Offer a varied diet: sinking catfish pellets or wafers, bloodworms, tubifex, frozen brine shrimp and daphnia, and high-quality dry foods. Feed primarily in the evening, when the fish are most active, and avoid overfeeding.
Breeding Hoplosternum thoracatum
Breeding this species is one of the most rewarding experiences it offers. Spawning often occurs spontaneously in a community tank without any special preparation.
Triggering spawning. A gradual temperature drop of 2–3 °C followed by a return to normal levels, combined with a partial water change using softer, slightly acidified water, will usually stimulate spawning behaviour.
Bubble nest construction. The male constructs a floating foam nest on the water surface — typically under a broad floating leaf, beneath the tank cover, or near a filter outlet. The foam is produced from mucus and air. This behaviour is strikingly similar to that of labyrinth fish, though Hoplosternum thoracatum is not related to them. Interestingly, you can also observe similar bubble-nest building behaviour in species like Betta during their own breeding rituals, though the mechanism is entirely different.
Spawning and parental care. The female deposits eggs into the nest, which the male fertilises and then guards with great dedication. He retrieves fallen eggs, removes unfertilised ones, and repairs the nest as needed. At 25 °C, larvae hatch in approximately 96 hours. If spawning occurred in a community tank, it is advisable to carefully transfer the nest to a separate grow-out tank on the second or third day, using a wide bowl or deep plate slid gently beneath the nest.
Raising fry. Start with infusoria and micro-organisms. As fry grow, introduce freshly hatched brine shrimp nauplii, micro-cyclops, and daphnia. Regular partial water changes in the grow-out tank are essential.
Biological Summary Table
| Characteristic | Data |
|---|---|
| Scientific Name | Hoplosternum thoracatum (Valenciennes, 1840) |
| Family | Callichthyidae |
| Native Range | S. America (Amazon, Orinoco, Paraguay, Trinidad) |
| Wild Length | up to 22 cm |
| Aquarium Length | up to 18 cm |
| Sexual Dimorphism | males slimmer, thicker pectoral spine |
| Sexual Maturity | ~18 months |
| Respiration Type | gill + intestinal air breathing |
| Spawning Type | foam nest, male guards |
| Incubation | ~96 hours at 25 °C |
| Diet | omnivore, bottom feeder |
FAQ: Common Questions About the Hoplo Catfish
Why does my Hoplo Catfish keep swimming to the surface and gulping air — is something wrong?
Nothing is wrong — this is completely normal behaviour. Hoplosternum thoracatum has a specialised intestinal respiratory organ that allows it to extract oxygen from swallowed air. This is an evolutionary adaptation to life in warm, oxygen-poor shallow waters. If the fish seems to surface unusually frequently, check dissolved oxygen levels and water quality.
Can Hoplosternum thoracatum be kept with small fish?
Absolutely. This species is entirely peaceful and shows no aggression toward any tank mates, regardless of size. It is focused entirely on foraging along the substrate and ignores other fish completely.
How do I tell male and female Hoplo Catfish apart?
Males are noticeably slimmer than females and have a thicker, more robust first pectoral fin spine that may develop an orange tint during the breeding season. Gravid females appear noticeably rounder in the belly.
My Hoplo keeps uprooting plants — what can I do?
This is natural digging behaviour during food searches. Use potted plants, choose species with strong root systems, or anchor plants with rocks. Regular feeding also helps reduce excessive digging.
How long does the Hoplo Catfish live?
With good water quality, a varied diet, and compatible tank mates, Hoplosternum thoracatum can live 8–10 years in captivity.
References:
– Reis, R.E. (1998). Systematics of the Neotropical catfish family Callichthyidae. Ichthyological Exploration of Freshwaters, 9(1).
– Froese, R. & Pauly, D. (eds.) FishBase — fishbase.se
Last updated: July 05, 2026
