Experts have revised the diagnosis for the Lake Malawi mbuna genus Metriaclima.
Ad Konings and Jay Stauffer revised the diagnosis of Metriaclima to include a number of feeding behaviour characteristics.
"Species of Metriaclima feed at almost perpendicular angles to the substrate", the authors wrote in the journal Ichthyological Exploration of Freshwaters.
" are able to align the teeth of both upper and lower jaws in the same plane by abducting the jaws to a 180-angle opening".
Konings and Stauffer believe that the teeth of Metriaclima comb through the algae anchored to the substrate while closing the mouth, allowing them to collect loose material.
The fish typically make a number of bites to the substrate in rapid succession. During the scraping process, Konings and Stauffer claim that nothing is actually torn from the substrate; the fish merely collects loose strands of algae and diatoms.
180 degreesThe revised diagnosis covering the 180-angle opening of the mouth also helps to differentiate Metriaclima from other mbuna:
"In this respect, Metriaclima distinguishes itself from the species in Pseudotropheus, Tropheops and Melanochromis because these are not able to neither open their mouths to a 180 angle nor do these rake the loose algae from the substrate."
Konings and Stauffer believe that Cyathochromis obliquidens feeds in a similar manner to Metriaclima, albeit from the leaves of aquatic plants, rather than from rocks.
Petrotilapia is also believed to feed in a similar manner from rocks, but is readily distinguished from Metriaclima by its tricuspid (three-pointed) teeth in the outer rows.
Metriaclima zebraKonings and Stauffer have also expanded the diagnosis of Metriaclima zebra to include a population which lacks distinct vertical bars.
A principal component analysis (PCA) statistical study of a pale blue form of M. zebra found at Maleri Island against the blue-black barred Metriaclima zebra found at Namalenje Island, suggests that the colour pattern in M. zebra is indeed variable and that the Maleri Island fish is a true zebra lacking the classic barred pattern.
For more information see the paper: Konings AF and JR Stauffer Jr (2006) - Revised diagnosis of Metriaclima (Teleostei: Cichlidae) with description of a new species from Lake Malawi National Park. Ichthyological Exploration of Freshwaters, Vol. 17, No. 3. pp. 233-246.