Radium doesn't emit light, it emits alpha particles. It only glows when you put it in something which converts the energy of the alpha particles into visible light.
How much Radium does a Cuttlefish actually hold? It'd have to obtain it from the water its in and it'd be very difficult to get it out of the fish, you'd still have to filter it from the ink. We have processes which filter it from water or can be obtained directly from Pitchblend (a Uranium ore) or other radioactive materials so why have all the hassle of having to farm huge quantities of cuttlefish inside radioactive water and then have the problem of getting it out of the ink.
But good job on both PP and CSS showing they don't even grasp basic physics or bother to do any research before shooting their mouths off.