Adobo, your buddy must be confusing it with some other aquarium screensaver. There are no plugins available for this one. (Although there's some horribly done russian hacks with messed up colors).
Also, I have to dissapoint you as I can guarantee you won't see any violence in "SereneScreen" Aquarium. However, a Leopard shark is considered for a later addition and a small octopus will be the finishing touch (in a distant future). The man behind the screensaver, Jim Sachs (used to make good-looking stuff for the Amiga) intends to make three more screensavers as a series, this one, a butterfly garden, a terrarium and finally an aviary with birds when video card technology has advanced a bit further...
/Tiny