Here's a quote that might lend some credence.
From 'Jimmy Page:Magus, Musician, Man' by George Case:
Chris Dreja-"I used to meet him outside, of all places, a tropical fish store in Tolworth," Dreja looked back. "Jimmy was a tropical fish enthusiast and he'd say something like, 'Hello, Chris, I've just bought a nice thermometer for my fish.' He was a strange guy, even then."
So yeah, I guess he's always been interested in fish!
(BTW Chris Dreja, dunno what is so strange about that)