This is one of the mormyrids, related to the elephant-nosed fish, which are known to use their weak electric organs to navigate in muddy waters. However I don't know which species.
ZTL lists the species at Porte Dorée as Brevimyrus niger, Campylomormyrus numenius, Marcusenius mento & Mormyrops anguilloides, although of course this list may be out of date and/or the species may not have been identified correctly (this is a difficult family of fishes, most of which are rarely or never imported): comparing these names with the images from FishBase and Google, I don't think any of these names match the fish in this photo.
Perhaps it might be Mormyrus kannume or Mormyrus rume which is imported from Nigeria occasionally and has spawned in aquaria.
