Malawi Eyebiter (Dimidiochromis compressiceps)
Africa’s Lake Malawi is home to an enormous variety of ecologically and behaviorally distinct cichlid groups. There are the “mbuna” that dwell among the rocks, scraping off a diet of algae, detritus, and invertebrates. There are the “utaka” that live in the open water picking off plankton with their specialized tube-shaped mouth. And then there are all the other genera that don’t fall into either of these groups, sometimes referred to informally as “Haps” after the group to which they belong, the Haplochromini.
Included here are species that tend to occur away from the rocky shoreline, but without the specialized adaptations of the utaka. Some are peaceful micropredators on invertebrates (Otopharynx, Protomelas), while many others are more predatory. Among these is a fish known evocatively as the Malawi Eyebiter, Dimidiochromis compressiceps.
At up to ten inches in length, this beautiful, shiny blue species makes for a stunning addition to a peaceful Malawi-themed aquarium, but care has to be taken to avoid any unintended predation. This fish boasts a surprisingly large mouth and is capable of feeding on fishes nearly half its size. They do so with an unusual set of physical and behavioral adaptations.
The species name “compressiceps” references the slender, compressed body of this fish. When seeking out prey, Dimidiochromis will approach its intended victim from the side at a 90 degree angle, head pointed downward. More often than not, the unlucky prey won’t even notice its in danger, as the combination of a thin body, cryptic coloration, and its adept hunting strategy effectively blends Dimidiochromis into the watery vastness of Lake Malawi. A quick snap of its jaws and the prey is engulfed. However, sometimes an eye is all that is taken. Why this is so is debatable, and the true prevalence of this “eyebiting” behavior in the wild is perhaps debatable.
Out of the incredible speciation that has taken place with Malawi’s cichlids, Dimidiochromis appears to be most closely related to another ambush hunter, Nimbochromis, most famous for the lethargic hunting strategy observed in N. livingstonii.
Given its large size, an equally sizable aquarium is called for if housing Dimidiochromis. While this species can certainly be kept with other large, robust freshwater fishes, it looks most appropriate in a biotope based on its Malawi home, compete with a sandy bottom and large, rocks, perhaps with a bed of Vallisneria to help conceal its presence. Good tankmates would include Aulonocara peacocks, sandsifting Lethrinops, utaka like Copadichromis, as well as some of the other groups already mentioned. Mbuna are potentially too aggressive for this retiring predator, though more peaceful options like Labidochromis caeruleus can prove suitable.