Go for fillings.

      Teeth normally have lines and pin point depressions on chewing surfaces. We call them as pits and fissures which are normal . For some people these pits may be little deep, lodging some food debris if proper tooth brushing is not done, leading to decay.        In your case pits and fissures are stained due to food which is normal I think.        But it is equally important to visit a dentist who will probe the pits using a dental equipment and evaluate if it is pit and fissure caries. So it is advisable to visit a dentist every 6 months to prevent  decay.