hm...

you don't get something useful, but its nice to know you saved his precious live*lol*

You can save him while feeding him with 2 kind of fish!
There are 4!

"yummy fish"
"just a fish"
"rotten fish"
"fish"

yummy fish is a very fast swimmer and he's the best for Cid so try catch him!

Its difficult to divide "just a fish" & "rotten fish", but I think jaf's swimming a lil bit faster!
just a fish is also good for Cid, but rotten fish make's him feel worse.

the worst fish you can get is the very slow "fish".
feed him to Cid and he feels MUCH worse!

If there are just the two worse fish swimming in the sea, go to Cid , talk to him and return. Now there are others swimming around.

Lets say there is a "point system" for feeding Cid.

feed him with yummy fish: +2
feed him with just a fish : +1
don't feed him : -1
feed him with rotten fish : -2
feed him with fish : -3

Its a long trip to make Cid feel better. I'd prefer to kill him because of the funny suicide scene of Celes