Fishin’ Blues is one of the most widely recorded country blues songs.
Betcha goin’ fishin’ all of your time, baby’s goin’ fishing too
Bet your life, your sweet life, catch more fish than you
Many fish bites if ya got good bait
Here’s a little tip I would like to relate
Big fish bites if ya got a good bait
Song is about a catfish, probably more songs about catfish than any other swimming critter. A real classic is Muddy Waters doing I Wish I Was A Catfish.
“The Fish (Schindleria Praematurus)” is built around a bass solo by Chris Squire (each of the five members of the band had “solo” songs on that album), and “Fish” was Squire’s nickname.
“Shark Attack” by Surf Punks
“Hammerheads” by Shriekback
“Oh, the shark has pretty teeth, dear
And he shows them, pearly white”
Okay, I know the song isn’t about fish. I’m only submitting it because of its first two lines.
I’m sorry, that is about an amphibian.
Anything by Billy Ocean.
Schubert’s “The Trout”
Mr. Bass by The Descendants.
It’s not about — or pronounced like — the stringed instrument.
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“Under the Sea,” from The Little Mermaid. Of course, I like Homer’s version better.
It was years after the album came out that I was told what Anderson is singing at the end of, “The Fish:” it’s the sub-title; of course, the meter is atrocious.
WTH does Tell the moon-dog, Tell the March-hare mean, anyway?
Done! This is absolutely the thread winner. Congrats.
In early 90’s, San Francisco Bay Area, there was a local prog rock band called Episode. Their second album contains an out-of-place ditty called “Dead Fish in the Tank,” clocking in at 1:40.
This is so obscure, I am stunned that I was able to find a live recording of it!
The Five Pound Bass by Robert Earl Keen
Primus - Ol’ Diamondback Sturgeon
https://m.youtube.com/watch?v=YNGpNP6qud0
“The Ol’ Diamondback Sturgeon came swimming along, minding his business one day.”
Hey, by Anderson’s standards, those are pretty good lyrics. 
(And, I say this as a long-time Yes fan.)
“Su-Su-Sushi” by the Tubes
“Boudrieaux Was a Nutcase” by the Austin Lounge Lizards (It’s the story of Moby Dick, set in a Louisiana lake, a guy trying to catch a large-mouth bass.)
“Yellow Back Fly” by Steve Martin and the Steep Canyon Rangers (Same story, but more laid back)
“Lump” by Presidents of the United States (This one might also fit under “Songs about Groupies”)
“Barracuda” by Heart
Nobody’s mentioned Country Joe yet ???
Gimme an F!! …
As it should be.