The edible crab was originally caught by a fisherman in Dartmouth who then drove it on to Weston-super-Mare in the back of his car.
With its hand-sized claws and 9in shell, the massive crustacean was such a fine specimen the fisherman decided to present it to a sick friend in the hope it would cheer him up.
The crab then spent five days in the fridge.
However, when it came time to cook it, the family decided they could not bring themselves to do it, and instead they contacted Bristol Aquarium.
David Waines, from the aquarium, said: "We received a phone call from a lady who told us they had a large crab in their fridge and they wanted to donate it to the aquarium. Basically, they didn't have the heart to kill him.
"When she told me it had been in there for five days, I couldn't believe it was still alive. I told them to wrap it in a wet towel and bring it along to the aquarium as quickly as possible.
"We placed it into a special tank in our quarantine area and began pumping oxygen-rich seawater over it and it immediately started to show signs of recovery. Hopefully it will enjoy an unexpectedly long retirement."