Big Sea Crab

I caught a sea swimming crab that is rather large.  It may be small for eating but big for aquarium.  I took it home to see how long it can survive in my tank.  I find the water in my small tank in the living seems a little toxic to the fishes I caught.  So I change the water almost totally.  It seems the fishes are doing quite well except I do not know how long they will last without food from the sea.  The swimming crab is in the large tank outside and may survive longer as there are quite a few creatures in there including a large hermit crab and many prawns.  Catching live fishes is quite tiring as it requires fast reflexes and a lot of bending down.  It is good for back exercise and core muscles.  I should strengthen back and core so that I do not get so sore after my "catching" session.