this configuration is in artio joomsef control panel
login joomla administration control panel, then
component -> ARTIO JoomSEF -> ARTIO JoomSEF Configuration
scroll down the page and find "Advanced configuration" , you will find "Reappend source (Itemid)"
default is 'yes', just set to 'no' then itemid?xxxx will be gone on the url path
by the way, I like to thanks ARTIO which developed a free sef which is compatible with joom!fish. Before I found this artio joomsef, I use open-sef and had sepnd many hours to find a solution to work with joom!fish but didn't at the end. At least current latest open-sef 2.0 RC5 SP2 still not compatible with joom!fish