Fiddler crabs need land. They spendmost of their time on land and little time in the water. I had some and I had no clue they needed land, till it was too late. They kept escaping and I kept putting them back in. I made them drown. I felt so bad...Could get a crayfish. As for a rope fish in a 10 g, I would not suggest it. I have one and when I first got it, I put him in my 10 g and realized how cramped up he was and moved him to my 30 g.....much happier there. Get ya some african clawed frogs. I have 4 of them. Not the dwarf kind. They will tear up the feeders