Try reloading the aliases.ini file
Note that, by default, mIRC uses /q <nick> to start a query/pm conversation with that nick. This has nothing to do with fish keys.
To reload the aliases.ini, I recommend that you follow these steps.
1) Open mIRC
2) Type //copy $nofile($mircexe) $+ defaults\scripts\aliases.ini $mircdiraliases.ini
3) Type //load -a $mircdiraliases.ini