Pseudotropheus flavus was initially classified as Ps. elongatus sp. "dinghani," but upon further study of its morphology and habitat it was suggested that this fish was indeed a separate species. Consequently, it received its own species classification. Notwithstanding, Ps. flavus is still considered a member of the Pseudotropheus elongatus complex.
Ps. flavus is limited to the small island of Chinyankwazi, Lake Malawi. This fish was apparently imported in the late 1970s but subsequently disappeared from the hobby until more recent introduction. To my knowledge, this fish has not been exported since 1985, due to the collection restrictions placed on the area as it is part of the National Falls Park. This is too bad, as most of the strains I have seen have muddied or muted colors from prolonged inbreeding.
Note: Since writing this, it appears exportation has resumed, perhaps from a different part of the lake. It's also not unheard of for a little money to exchange hands to allow some divers a few hours within the Park's borders. Who knows.
As one might imagine, Ps. flavus are a lot like Pseudotropheus elongatus, both in size and shape, not to mention temperament. Males are unusually territorial, hunting for food around their own claimed rock, and defend their district against any intruder. It is suggested that males be kept with females in a ratio of 1 male to 3 or even four females. This is because males are very aggressive to one another and females do not group together. Ps. flavus is best kept in an aquarium of 75 gallons or larger.
The males of this rare species are very colorful, but the females tend to be a dingy mix of shaded yellow to brown. This mbuna also grows long and slender. In the wild, it usually grows to a maximum of 3 inches (8 cm) in length, males being a slightly larger than females. Because of their smaller size they have been grouped among the Pseudotropheus dwarf species. In captivity, however, this fish can easily reach a maximum length of 4 or 5 inches (10 - 12.5 cm). In my experience, they begin to show their adult coloration at as early as 2 inches (5 cm). In the wild, Ps. flavus is found among the sedimentary rocks of Chinyankwazi Island's reef, at a depth of 7 to 20 m. This mbuna is an omnivore, subsisting primarily upon the plankton in the open water and the algae that grows on rocks. For the aquarium, I recommend a Spirulina-based flake food.
Males tend to be moody in their coloration, not always displaying the bright yellow coloration. It can also take them a while (and in the company of females) to color up brilliantly. On an interesting note, one night after the lights had been turned off for several hours, I purposefully turned on the lights in the room with the intent of catching some fish in the same tank as my Ps. flavus. Of course, everyone in the tank was asleep on the gravel, but to my surprise, everyone - including my three females - were all colored up with the bright yellow! As they began to wake up, the females turned off the yellow, going back to the brownish color, while the male kept his yellow. I am certain of their gender as these three females have each laid eggs. □