This a 'Marmalade cat', which is male mbuna of an OB morph (short for Orange Blotch). Unfortunately several species have this morph, in which the normal colour pattern is replaced by irregular dark blotches on an orange background. This is much commoner in females - like the one in the other photo. Most adult male mbuna are blue, but unusual OB males like this one have a blue sheen over the orange background - the term 'Marmalade cat' is said to an anglicisation of the native word namakate which is used for all the OB mbuna.
It is harder to say which species this fish belongs to, because the OB markings replace the normal colouration, but based on the body shape I would suggest Maylandia zebra (noting the alternative generic names of Pseudotropheus and Metraclinia). Zootierliste indicates that Antwerp holds this species.
@gentle lemur Thank you very much for your insight and information, Gentle lemur.
I did not know about the orange blotch and Marmalade cat morphs in mbuna/Lake Malawi cichlids so that's pretty interesting to learn about.
I did a bit of research and I found photos of fish that looked very similar to this labeled as Maylandia - and Zootierliste in fact also has pictures of fish that look very similar to the ones I saw.
