Diplotaxodon

Genus Overview: Diplotaxodon (Big-eye Haps)

The genus Diplotaxodon comprises highly specialized, silver pelagic predators endemic to Lake Malawi. Biologically unique, these fish occupy the vast, open-water pelagic zones and deep benthic shelves—frequently documented at depths exceeding 50 to 200 metres, where light is almost non-existent.

Low-Light Visual Adaptations & Upturned Jaws

The name Diplotaxodon translates from Greek to mean "double row of teeth," a reference to their specialized internal oral dentition. Because they survive in cold, high-pressure, dim, or pitch-black layers of the lake, they have evolved massive, prominent eyes with highly light-sensitive retinas. This acoustic-visual adaptation allows them to hunt by silhouette, tracking down schooling sardines (Engraulicypris sardella, locally known as Usipa) or deep-water invertebrates from below.

To support this vertical hunting style, they feature heavily upturned, almost vertical lower jawlines. This structural angle allows them to scoop up fast-moving open-water prey above them with incredible efficiency while cruising in deep-water currents.

Valid Species Directory

Modern ichthyology recognizes roughly nine valid species within this specialized lineage, though deep-water research continues to log additional variations:

• Diplotaxodon aeneus Turner & Stauffer, 1998
• Diplotaxodon apogon Turner & Stauffer, 1998
• Diplotaxodon argenteus Trewavas, 1935 – The type species of the genus, highly silvery and aerodynamic.
• Diplotaxodon ecclesi Burgess & Axelrod, 1973
• Diplotaxodon greenwoodi Stauffer & McKaye, 1986 – A heavily studied deep-water predator.
• Diplotaxodon limnothrissa Turner, 1994
• Diplotaxodon macrops Turner & Stauffer, 1998 – Characterized by exceptionally massive eyes.
• Diplotaxodon oligodontus Snoeks, 2004
• Diplotaxodon similis Turner, 1994

Aquarium Considerations

Due to their strict deep pelagic water requirements, Diplotaxodon species are incredibly rare in the standard home aquarium trade and are usually only housed by specialized public aquariums or dedicated biotope institutions. In captivity, they demand expansive tanks (6 to 8 feet minimum) focusing purely on open horizontal water volume.

Highly oxygenated, pristine water conditions are an absolute necessity. To replicate their native habitat and protect their delicate, large eyes from stress, lighting should be kept intentionally dim or filtered, and they must never be housed with rowdy rock-dwelling Mbuna.