My first thought was a Melanochromis species, but there is zebra cichlid that might be a better match, Maylandia sp 'Msobo'. I can't really tell from this angle. All the blue fish are males, but if they are 'Msobo' there should be some big females nearby which would be plain bright yellow.
@gentle lemur
A better angle is not really possible, these fish are in the water of the Nile crocodile enclosure which can only be viewed from the top.
I was also thinking of a Melanochromis species, maybe the M. cyaneorhabdos or the M. johannii.
There are also yellow fish, but i'm not sure if those are from the same species. There are also other species in this there.
The fish do have a sign. The sign says 'Malawi cichlids' and mentions the following scientific names: Metriaclima lombardoi
Labidochromis caeruleus
Labidochromis sp.
@MennoPebesmaPseudotropheus cyaneorhabdos, which was suggested by @Kakapo for your other image, is certainly a possibility: the label suggests that the zoo thinks that this is right and they ought to know because in this species males and females look very similar. On the other hand, the head shape and coloration don't quite match the photos of this species that I have seen. Maylandia lombardoi (I'm afraid the genus names keep changing) reverses the usual colour patterns by having bright yellow males and BB females (BB meaning the common colour pattern of blue and black bars). This is quite distinctive in adult specimens. Labidochromis caeruleus is confusing in a different way: males and females are coloured identically, but they are bright yellow or pale blue or almost white in different localities in the Lake, most have a wide black stripe along the dorsal fin (but not all). Labidochromis sp. is a cop-out.
