I should have commented on this image before.
This species is undescribed at the moment. It is endemic to Lake Chilingali, a small satellite lake near Lake Malawi, but that lake is vulnerable to environment change and contains some introduced species, so it may be endangered or even extinct in the wild.
This individual is an adult male, roughly 10cm long. Its barred pattern appeared when it was approached by the dominant male in the tank, which is slightly larger and always has a plain silvery body. There are several species of Rhamphochromis in Lake Malawi, where some of them grow to more than 40cm long. Aquarists sometime call these fishes 'silver bullets'.
