Hi i hope you find that Black Goliath, but in my opinion i believe these Black Golaiths are the same as the ones we all know but due to their habitat being a bit different they acquire a darker colouration, but i also believe that they probably only acquire the darker colour when they reach at least 2 foot or more in size and if you notice the pics of the black Goliaths they are still that golden brown colour nearer the middle and bottom and only really black on top, this is usually for camouflage as the river is probably darker there, not sure but ive noticed this in other species as everything in nature tends to adapt to its surroundings. So i would imagine if put in an aquarium it would slowly lose its black colour?????
" 