This is the original file from 1998: https://git.gnome.org/browse/gnome-panel/tree/applets/fish/fish.c?h=GNOME_0_20
And here’s the file header, typos and all
/* fish.c - The msot useless applet, it's an ugly fish drawing
* by the least sane person, yes you guessed, George, it's nice
* to break the monotony of finals
*/
I’ll leave the eyes as an exercise for someone else.
I don’t know who George is. I first encountered Wanda (as the fish is known now) many years ago when first exploring Linux, and more recently I’ve had to dive more deeply into her source while working on MATE