I found an interesting ascii aquarium screensaver for Linux terminals called Asciiquarium.
I installed it tonight and took some screenshots:
A ship, castle and goldfish:

A whale:

A large shark:

A sea monster:

Asciiquarium is a short Perl program that runs in a terminal. To download it, make sure that you have Term::Animation. On Ubuntu Linux, that means typing sudo cpan and then install Term::Animation.
The go to your downloaded Asciiquarium file (it's just a Perl program in text format) and chmod +x in a terminal to make it executable. Then type ./asciiquarium to start the program.
There is also a version of Asciiquarium as a KDE screensaver. There is also a version for Mac called MacAsciiquarium. Check it out!
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