Rondoni Sand Knifefish

Gymnorhamphichthys rondoni is a member of the family Rhamphichthyidae — the sand knifefishes — a group of weakly electric Neotropical fish related to the more familiar ghostknifefishes but with quite different ecology. It is a slender, elongated fish with a distinctly prolonged snout and lacks a dorsal fin, relying on a long, undulating anal fin for propulsion. Its most remarkable behaviour is burying itself completely in fine sand during daylight hours, emerging to hunt benthic invertebrates after dark.

In the aquarium Gymnorhamphichthys rondoni requires a deep layer — at least 10–15 cm — of very fine, smooth sand substrate into which it can burrow. The tank should be minimum 150 litres with soft, slightly acidic water, tannin staining, and very gentle filtration flow to avoid disturbing the sand. It is a peaceful, non-aggressive species that will not disturb other fish and can be kept alongside other small to medium peaceful SA bottom-dwellers.

Feeding should be timed for evening or night and consist of frozen bloodworm, frozen or live Tubifex, and small invertebrates placed on the substrate surface. It is one of the most specialised and fascinating South American fish available to the hobbyist and rewards patient, observant keepers who can meet its specific needs.

Water: Soft, pH 4.5–7.0, 24–28°C; gentle flow; tannin staining; very fine sand essential. Tank: 150 L minimum; 10–15 cm deep fine sand; dim lighting; evening feeding. Feeding: Nocturnal benthic predator — frozen bloodworm, Tubifex, small invertebrates; feed at lights-out. Breeding: Not documented in captivity. Compatibility: Peaceful; co-exists with small to medium peaceful SA species; do not keep with gravel-disturbing fish.