Aquarium knifefish and bichirs: shape, movement and adult needs

Black ghost knifefish, left-facing adult natural-colour AI side-view illustration

Black ghost knifefish50 cm TL · source record; typical adult TL unknownBlack knife-shaped body, a pale forehead line and two pale tail rings; a long anal ribbon fin runs below the body, with no ordinary dorsal fin.

Alligator gar, adult natural-colour left-facing AI illustration

Alligator gar305 cm SL; 300 cm unspecified · source records; typical adult TL unknownA heavily armoured, stout gar with a short broad snout, olive-grey adult body and spotted rear fins.

Royal featherback, adult natural-colour left-facing AI illustration

Royal featherback120 cm SL · source records; typical adult TL unknownSmall dark dots on the front flank merge into irregular oblique stripes toward the tail, continuing onto the rear fins.

Clown featherback, adult natural-colour left-facing AI illustration

Clown featherback100 cm SL · source records; typical adult TL unknownA deep silver fish with large pale-ringed black spots above the rear anal-fin base; the number of spots varies.

Indonesian tiger perch, adult natural-colour left-facing AI illustration

Indonesian tiger perch50 cm SL · source records; typical adult TL unknownOften grayish yellow, with numerous broad dark bars; stress and night colours can obscure the pattern.

Siamese tiger perch, adult natural-colour left-facing AI illustration

Siamese tiger perch40 cm SL · source records; typical adult TL unknownAdults often have orange-yellow ground colour with usually four, occasionally five broad dark bars; stress can darken the whole fish.

AI illustration of Erpetoichthys calabaricus, complete left-facing side view

RopefishTypical adult total length unknownRope-like body with olive-brown back, yellow-orange belly and a dark pectoral-base patch; lacks the pelvic fins found in Polypterus.

AI illustration of Gnathonemus petersii, complete left-facing side view

Peters's elephantnose fishTypical adult total length unknownDark body with pale curved rear markings; the projecting 'trunk' is a lower-lip extension, not a nose on top of the head.

South American lungfish, adult natural-colour left-facing AI illustration

South American lungfish125 cm SL · source records; typical adult TL unknownA long, eel-like lungfish with slender short paired fins. Adults are often uniformly brown; juvenile gold spots do not represent adult colour.

Florida gar, adult natural-colour left-facing AI illustration

Florida gar[33, 86] cm TL; 133 cm TL · source records; typical adult TL unknownA slender armoured fish with dark spots on an olive-brown body and fins; dorsal and anal fins sit close to the tail.

Peacock spiny eel, adult natural-colour left-facing AI illustration

Peacock spiny eel20 cm SL · source records; typical adult TL unknownAn elongated brown fish with a projecting rostrum, small pectoral fins and pale-ringed dark rear dorsal eyespots; pelvic fins are absent.

AI illustration of Mastacembelus erythrotaenia, complete left-facing side view

Fire eelTypical adult total length unknownA long dark brown fish with red-orange lines that break into rear spots, a pointed rostrum and small pectoral fins.

Indian glassfish, natural-colour adult male, left-facing AI illustration

Indian glassfish8 cm unspecified; 8 cm SL · source records; typical adult TL unknownA laterally compressed translucent fish with visible internal outlines. Males may show naturally blue dorsal and anal margins, distinct from artificial dye.

Armoured bichir, left-facing adult natural-colour AI side-view illustration

Armoured bichir35 cm SL · source record; typical adult TL unknownGray-green body with 7–8 dark vertical bars of variable thickness, 10–13 dorsal finlets and a relatively small mouth.

Saddled bichir, adult natural-colour left-facing AI illustration

Saddled bichir75 cm SL; 75 cm TL · source records; typical adult TL unknownBroad flattened head with a projecting lower jaw; irregular dark saddle bands fade toward a paler belly.

Ornate bichir, adult natural-colour left-facing AI illustration

Ornate bichir60 cm SL; 60 cm TL · source records; typical adult TL unknownComplex black-and-yellow patterning extends into the fins; finely patterned head, projecting upper jaw and separate dorsal finlets.

Senegal bichir, left-facing adult natural-colour AI side-view illustration

Senegal bichir50 cm SL · source record; typical adult TL unknownAdults are gray-brown to olive with a pale underside, without juvenile horizontal stripes; 8–11 separate dorsal finlets and a slightly projecting upper jaw.

West African lungfish, adult natural-colour left-facing AI illustration

West African lungfish100 cm SL · source records; typical adult TL unknownA stout elongated fish with filamentous paired fins and a blunt head. Its variable blotches cannot identify African lungfish species alone.

African knifefish, left-facing adult natural-colour AI side-view illustration

African knifefish30 cm SL · source record; typical adult TL unknownBrown knife-shaped profile without a dorsal fin; the anal and caudal fins form a continuous ribbon.

Aquarium knifefish and bichirs: shape, movement and adult needs

An entrance for distinctive outlines

Knifefish, bichirs and other distinctive fish share this browsing entrance for readers who do not yet know a name. They are not one family with a common care plan. Apteronotus albifrons and Polypterus senegalus are two starting points; follow the scientific identity after recognising an outline.

Black ghosts: undulating movement and weak electric sensing

Black ghost knifefish move with undulating fins and can swim backwards. They use a weak electric field to sense their surroundings and find food. Daytime visibility alone is not a complete assessment. Provide subdued areas and cover, plan adult accommodation, and account for small-fish predation and potential conflict with their own kind.

Bichirs need both floor space and surface access

Senegal bichirs need usable bottom space and shelter while retaining access to air at the surface. Secure covers prevent escape; the layout must still allow ascent. This predator cannot be assumed safe with fish it can swallow. Consider food, adult size and usable accommodation together, rather than merely finding a cavity that fits the body.

Look beyond the juvenile silhouette

Continue to the black ghost profile for its movement and cover needs, or the Senegal bichir profile for space, breathing and escape prevention. Their juxtaposition compares features. Other unusual fish still require individual assessment; bottom-dwelling or nocturnal labels cannot replace questions about diet, accommodation and tankmates.

Sources

Knifefish, bichirs and more

Aquarium knifefish and bichirs: shape, movement and adult needs

An entrance for distinctive outlines

Black ghosts: undulating movement and weak electric sensing

Bichirs need both floor space and surface access

Look beyond the juvenile silhouette