Can you put a betta fish with crab?

No, you should not put a betta fish with a crab. While some species of crab, such as freshwater hermit crabs, may be able to coexist peacefully with betta fish in a large, well-planted aquarium, most crabs are not suitable tank mates for betta fish. Crabs are more likely to attack and kill the betta fish, or compete with them for food and resources. Additionally, some crabs, such as fiddler crabs, may be able to escape from the aquarium, which could pose a safety hazard.