Colomesus asellus

A Little More Information...

Colomesus asellus, also called Amazon Puffer, is a small freshwater pufferfish recognized by its rounded body, contrasting mask and active swimming style. Native to the major Amazonian river systems, it mainly inhabits calm or moderately flowing areas where it searches for small prey among sand, leaves and roots. Its care requires stable, well-oxygenated water and a varied diet based on meaty foods. This wild-collected species remains fairly common in the aquarium trade, but it is not an ideal choice for a standard community aquarium because of its tendency to nip fins.

General species description

Colomesus asellus belongs to the family Tetraodontidae and is one of the strictly freshwater South American pufferfish. It is distinguished by its compact body, relatively broad head and mobile eyes, which give it an alert appearance. Like other tetraodontids, it has fused dental plates adapted for crushing shells and exoskeletons. Its constant activity and open-water movements make it fascinating to observe. It may be kept alone or in a small group in a spacious aquarium, provided interactions are monitored. Tank mates’ fins are at risk, especially when the other fish are slow-moving or long-finned. An aquarium with sturdy plants, hiding places and broken lines of sight can help reduce chasing. This is a freshwater pufferfish, not a species that routinely requires salt to be added to the water.

Geographical origin and habitat

The range of Colomesus asellus covers a large part of the Amazon Basin, including areas connected with Colombian waters and the major tributaries of the Solimões-Amazon system. In Colombia, it is associated with the Amazonian region around Leticia and waterways linked to the Solimões-Amazon network. It inhabits side channels, backwaters, floodplain areas and forest margins that become flooded seasonally. Water may be clear, lightly stained or rich in suspended sediment depending on the season and proximity to floodplains. The habitat generally combines a sandy or muddy bottom with leaf litter, roots and submerged branches. Current speed ranges from slow to moderate, with stronger flow during high-water periods. Depth varies, but the species often uses shallow to intermediate areas where vegetation and debris provide shelter while leaving open swimming space.

Precise locality and local name

In Colombia, Colomesus asellus is mainly associated with the Colombian Amazon region, particularly the Leticia area and the tributaries and backwaters connected to the Amazon River. Its natural range extends well beyond a single site, which explains the differences in coloration and pattern observed among some populations. The English common name Amazon Puffer is widely used in the aquarium hobby. In Spanish, the descriptive name pez globo amazónico is used; in French, poisson-globe amazonien is the clearest equivalent. Vernacular names may vary between countries, local markets and river communities. In practice, reliable identification depends mainly on the scientific name, stated provenance and examination of the banding pattern. For a wild specimen, it is best to retain collection information, including country, basin and river when available, because these details help clarify its ecological requirements.

Appearance and physical characteristics

The body of Colomesus asellus is short, deep and slightly compressed, with skin lacking true scales. The base color ranges from grayish brown to olive yellow, with several clearly visible dark transverse bands across the back and flanks. A dark mark crosses the eye region, while the belly is generally paler. The fins are transparent to slightly yellowish and provide precise swimming, supported by rapid movements of the pectoral fins. Its beak-like mouth has teeth capable of breaking the shells of small snails and other invertebrates. Like other pufferfish, it can take in water or air when severely stressed, but this reaction should never be induced. Its adult size is moderate, but this does not mean that a small aquarium is appropriate: its activity, need for exploration and possible fin-nipping behavior require generous space.

General diet

In the wild, Colomesus asellus mainly eats shelled or hard-bodied invertebrates, along with various small aquatic prey. Snails, mussels, shrimp, worms and crustaceans are suitable foods. Hard foods are important because they support the natural wear of its continuously growing teeth. In aquaria, offer cultured snails, mussels, shrimp, krill and worms, varying the food size according to the fish. Some individuals may accept pellets, but pellets should not be the only food. Frozen foods must be high quality and offered in reasonable portions to avoid water pollution. Juveniles generally feed more often than adults, while mature fish should receive meals suited to their activity level. Avoid an exclusively soft diet with few shells, as well as overfeeding. A varied diet supports good condition and helps maintain appropriate tooth wear.

Essential data

• Native river name: Amazonian river system; the aquarium trade may include fish from several tributaries.
• Local name used: pez globo amazónico; Amazon Puffer in English.
• Origin of the scientific name: Colomesus is a genus name of Greek origin; asellus is a Latin term associated with a small donkey.
• Etymology of the full name: Colomesus identifies the genus; asellus is the specific epithet and means small donkey in Latin.
• Common/vernacular names: Amazon Puffer, Amazonian freshwater puffer, pez globo amazónico.
• Family: Tetraodontidae.
• Subfamily: Tetraodontinae.
• Name pronunciation: koh-loh-MEE-soos ah-SELL-oos
• Discovery: Johannes Müller and Franz Hermann Troschel, 1848.
• Maximum adult size: about 15 cm.
• Water temperature and pH: 24 to 28 °C; generally pH 6.0 to 7.5.
• Watercourse appearance and surrounding vegetation: backwaters, side channels and floodplains, with sand, leaves, roots, branches and dense riverside vegetation.
• Typical tank mates: Corydoras agassizi, Geophagus altifrons, Hemigrammus rhodostomus, Pterophyllum scalare; aquarium compatibility is not guaranteed.
• Temperament and behavior: active, curious and usually lively; may bite fins and should be monitored with slow-moving or long-finned fish.
• Water depth: shallow to intermediate areas, especially margins, backwaters and flooded-forest zones.
• Sexual dimorphism: difficult to distinguish visually; no simple external feature is reliable in retail specimens.
• Bottom structure and flow: sand, mud, leaf litter and submerged wood; slow to moderate flow that varies with flooding.

In your aquarium

Success with Colomesus asellus depends on clean, stable and well-oxygenated water, a layout with shelters and open swimming space. Use a mature aquarium, perform regular maintenance and provide a varied meaty diet that includes shelled prey. Closely monitor the fins of other fish, since behavior may change with age, hunger or crowding. Never intentionally inflate the fish and handle it gently. Since this is a wild fish, gradual acclimation is especially important. With effective filtration, a suitable diet and carefully selected tank mates, this pufferfish can become an active and fascinating aquarium resident. Water stability and preventing fin nipping remain the two main priorities.