Hi,
the fish reminds me on a dark colour variant of
Pseudacanthicus spinosus which was imported with about 50 normal coloured
Pseudacanthicus spinosus to Germany around 1994. When stressed the fish brightened up even nearly to the normal colouration of
P. spinosus. However, when it died it maintained the dark colouration when preserved. Unfortunatly i lost the preserved fish when i moved to another house. Although i didn't take any countings to compare with P. spinosus, im pretty sure it was merely a colour variant.
Here is a (not very good...) picture.
Greetings... Achim