Tropical Crayfish

Black Ghost needs:
Minimum Tank Size: 50 gallons
Care Level: Moderate
Temperament: Semi-aggressive
Water Conditions: 73-80 ° F, KH 0-10, pH 6.5 to 7.0
Max. Size: 1 '6 "

crayfish needs:
55-70 degrees Fahrenheit. 72 degrees is the limit below (temp wise this is not a good match
Crayfish can be territorial, so I would say they would not make good tank mates. If you choose to try to stay together, then allow hiding.

good chance
but the fish is electric and can kill other things around it when it is threatened, and crayfish eat fish that is close enough to seize it

It depends if theres only 1 crayfish, it should be fine, but other fish may not be so theres little caves for crayfish and the knife, but you know my nrver crayfish ate all my goldfish Peacock

Firstly, a 50 gallon tank is too small for a fish Black Ghost. It will grow about 20 inches long, which means it could not even turn around easily in most tanks of 50 gallons.

Secondly, the Black Ghost knife fish is a predator stealth. That means it will wait for a chance to catch and eat crayfish (or any small fish), then eat it.