Itsounds like this may well be a tumor, if it bends further I'm sorry it may be better to euthanize .
Buy some Oil of cloves add about 20ml to a bucket of water and let the rudd gently pass over adding more if he is still breathing say another 10 ml.
We have a koi that has a tumor at the moment he is living with it and doing well but if he started to develppe it into a larger mass then I would do the kindest way possible to put him to sleep with my fisj anesthetic MS222 oil of cloves is also a recognised way of doing this sorry I cant say we can help anymore than we already have
rgrds
Dave