To me it looks like an Altolamprologus calvus "Chaitika". Look at these two pics...
Juvie
Subadult
It looks like something between these two stages of growth. I don't think it's a sumbu. It has spots all over its body whereas the sumbu has none. The sumbus also have a blue tint on their lips which yours lacks. All Altolamprologus will live in shells if they have the chance. Most of them spawn in shells however the Sumbu uses it as its main home but other Altolamps may use rocks etc.
Bruce
Juvie
Subadult
It looks like something between these two stages of growth. I don't think it's a sumbu. It has spots all over its body whereas the sumbu has none. The sumbus also have a blue tint on their lips which yours lacks. All Altolamprologus will live in shells if they have the chance. Most of them spawn in shells however the Sumbu uses it as its main home but other Altolamps may use rocks etc.
Bruce