Curiosity Corner

Some species, often possessing unique anatomical features or biomechanisms, exist only as a single family in the world of the aquarist - and sometimes also in the wild. For these reasons we have grouped them together on this double page.


The Indian knifefish or clown knifefish lives in Asia in slightly alkaline waters. It can swim both forwards and backwards, and tends to be nocturnal. Several species have proved marketable; one of them, Notopterus notopterus, which has only recently been successfully bred in captivity, is used as a food source in certain parts of the world. Size: 20-30 cm. •

Notopteridae Elephant Fish

Xenomystusnigri (Notopteridae)

The African knifefish is distinguishable from N. chitala by the absence of a dorsal fin, but resembles it in being a twilight species. Occasionally it emits a groan-like sound from the pneumatic duct, which links the swim bladder to the digestive tube. Size: 10-20 cm

Gnathonemuspetersii (Mormyridae)

Peters's elephant-nose uses its "trunk" to sift the substrate for food, preferably in darkness, as it is rather timid. The elephant-nose can emit weak - and quite harmless - electrical discharges. Size: 15-20 cm.

Pantodon buchh olzi• (Pantodontidae)

The butterfly fish is a surface-dweller, gulping down its prey (it has a preference for live food) with its yawning mouth. Sometimes aggressive, it can leap from the water. Its common name derives from its butterfly-like appearance as it swims with pectoral fins outspread. Size: 12 cm.

Eigenmannia Virescens

Eigenmannia virescens (Rhamphichthyidae)

The green knifefish originates from calm waters in South America, and therefore prefers soft, acid conditions. Another more or less twilight species, it appreciates live prey. Appears not to breed in captivity. Size: 20-30 cm. •



The coloration of the back and belly is absent in feral varieties of the glassfish (Chanda ranga). A practice current in SouthEast Asia consists of injecting the fish with chemical dyes. This is more than questionable - it is downright unacceptable and ought to be stopped. We suggest very strongly that you boycott the purchase of such specimens; in any case, the coloration achieved is not permanent.

• Chanda ranga (Centropomidae)

The natural habitats of the glassfish are hard, brackish waters in Asia. This is a peaceable species, but hard to breed. The female lays a hundred or so eggs in the fine-leafed foliage of certain plants. The tiny fry must be fed on infusoria of a suitable size. Size: 5-6 cm.

African Leaf Fish

Polycentropsis abbreviata (Nandidae)

The African leaf fish really does resemble a leaf - a camouflage used to outwit its enemies. Its deformable mouth means that it can swallow prey measuring up to half its own size. There are several related species; one of them, which belongs to the genus Monocirrhus, swims at an oblique angle, head down, and has a small barbel on its lower jaw. Size: 6-8 cm.

Mastacembelus sp. (Mastacembelidae)

Several color variants are sold commercially under the name of Mastacembelus or spiny eel. The long snout acts as an organ of touch: only the head remains sticking out when the fish buries itself in the sand for protection. It is best to keep only one specimen, otherwise there will be constant fighting. Be careful too that this species does not escape from the tank, as it is very agile. Breeding in captivity is impossible without hormone injections. Size: 20 cm. •

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