Ptychochromis ernestmagnusi is a species of fish cichlid only known from the Mananara du Nord River in northeastern Madagascar, but it is probably more widespread in that region. If so, it likely occurs in the Mananara-Nord Biosphere Reserve (near the town Mananara Nord), which would give it a level of protection. It can reach 14.7 cm (5.8 in) in standard length.