I was looking at my tetras today, and one looks skinny. Colour seems normal, it's eating, no red gills, the line is normal. It does seem to swim up and down a lot at angles, but I might just be paranoid. None of the others look strange in any way. The only real symptom is the skinniness.
Could it just be a female that reabsorbed eggs? One definitely looked gravid not long ago, and now I can't spot her. I just worry for my little fin-friends.