The type of fishing line is going to be very important, I can't find a reference to what kind was used for his testing. But according to further links on the Wikipedia reference to optical fiber mentions commercial plastic fiber's outer cladding is made of fluorinated polymers. This can be found in so called 'invisible' fishing line, as it's index of refraction is almost exactly the same as water. I think the key is to get two different layers to refract some of the light energy back down the cable. Probably only interesting to an experimenter.