A Melbourne veterinary clinic has taken drastic measures to save a goldfish's life, putting the little pet under the knife to extract a life-threatening tumour.

George the goldfish is again able to swim without pain following the surgery, which cost its owner $200, The Age has reported.

The fish had been unable to swim, eat or sleep properly with the tumour affecting its quality of life.

The operation was carried out by Tristan Rich at Lort Smith Animal Hospital in North Melbourne.

George the goldfish will swim another day after undergoing brain surgery. (Lort Smith Animal Hospital) (Supplied)

Dr Rich said George's owner was "quite attached" to her pet and refused to have him put down.

The procedure took about 45 minutes.

"It's a very fiddly procedure, and you have to be very careful about blood loss," he said.

He said a fish of George's size could only lose about half a millimetre of blood before running into trouble.

The pet fish can now swim properly and is enjoying life again. (Lort Smith Animal Hospital) (Supplied)

However, the operation was a success and George has returned home.

Dr Rich said, although he had only operated on fish about 10 times in his career, that people often asked for procedures to be performed on more unusual pets.