add shortcodes only when plugin is loaded

is there a way to add a filter so i can add shortcodes..

because now i’ve a filter on plugins_loaded for 3.1+ and a register_activation_hook for below 3.1, but isn’t that called more then once (for example when you go to the plugin page?)

or is this called only once??

so what i’m basically asking a filter that is only executed once when the plugin is activated..

Thanks in advance!