A group of African tetras would fit the bill, so depending upon what is available local to you, there are species like
Congo Tetra (Phenacogrammus interruptus)
Yellow tailed Congo Tetra (Alestopetersius caudalis)
African Red Eye (Arnoldichthys spilopterus)
Long-finned (Brycinus longipinnis
)
One-Stripe (Nannaethiops unitaeniatus)
From personal experience, try and obtain at least two females per male in the group of 6-9 fish. I started off with 12 unsexed Yellow-tailed last year, but the group "imploded" when they matured and all turned out to be males, inflicting vicious wounds on each other during dominance fights which sadly killed most of them despite extra water changes and Myxazin treatment ("mussels" adopted the final three last autumn, which last I heard thankfully behaved in his 6-foot tank). Having said that, A. caudalis are probably the most fiesty of the African tetras, but it is perhaps something worth bearing in mind.
Away from tetras, you could possibly consider African Three-Striped Catfish (Pareutropius buffei), a midwater diurnal catfish. They do like some water current and the length of your tank may create long term issues if it is less than 100cm. They would need a sizeable group of 10+ to give them confidence.
A couple of African Butterfly Fish could finish the African theme, residing on the water surface. Providing the upper water current is quite calm and they have some plants (mine lurk in floating Canadian Pondweed) and they have 30cm square per specimen, they will be happy enough.