Who did the author think was a ‘physiotherapist’?

Directions: Read the passage and answer the question that follows.

I’ve grown fond of my two fish. They swim to the side of the tank every morning to watch me put on the jug for breakfast, begging silently to be fed. The big silver fantail goldfish does somersaults, as if putting on a show for his meal. He is a beautiful iridescent white that shines with every colour of the rainbow as he darts around. His friend is a golden, sleeker model, with smaller fins and tail – built for speed.
Once, while cleaning their tank, I scooped them into a clean tank while I rinsed their home and replaced the weeds. The next day I noticed my beautiful fantail was sick. He moped at the bottom of the tank with none of his usual antics to get my attention. His little friend didn’t seem to mind – he ate all the food flakes while the fantail watched. A short while later, the sleeker goldfish began to nip the fantail on the fins, forcing him to move. At first I thought this was aggression towards a sicker fish, but I soon realised he was helping his buddy keep moving, to oxygenate his blood and help him heal. He’s a physiotherapist, I thought.