It's quite unlikely that the glowing was due to radiation, if it was radioactive enough to glow like that you would probably get serious radiation poisoning just from being near it, and the fish would have been unlikely to live for long enough to get to catchworthy size.  It's more likely that there were algae in the fish which phosphoresce, or there are other microorganisms which can glow in the same way, by taking energy in as one form and emitting it as light.

There definitely is a limit, because if you get too small then electrons can 'tunnel' between two wires which are too close together.  That limit is somewhere around 10-50 atoms wide.  There's a thing called 'redwall', where the semiconductor industry are making smaller and smaller microchips, with increasing numbers of transistors on them, but they predict that around 2012 they will no longer be able to make chips any smaller.

However, new technologies may yet find ways to shrink things even further.

Bulls eyes are dichromatic - they have two colour pigments in their retina.  They can see red, as well as being able to see other colours, but they would see things in a similar way to a colour blind person.  There's nothing special about red, its more likely to be that the bull is excited by someone wearing silly clothes, dancing about and flapping something in the bull's direction.  The bull is generally hot, bothered and fed up, but there's no evidence that there's anything special about the colour red.

The water coming out of a nuclear power station should be identical to that coming out of a normal power station, but it would be nice warm water.  Chris used to sail near the outlet of a power station and found the water so warm it was like a bath!  Because this water is so warm, they've found fish around UK power stations that you would normally find in the Mediterranean, which wouldn't survive a winter otherwise.  Also, the warm water encourages other marine species that the fish can feed on.