White gills?

[grant0]

I noticed today that my betta has developed strange light markings around his gills on both sides, as seen in the photo above. Any thoughts on what this might be? (And isn't my fish beautiful? Hehe.)

Questions from the sticky:

– My tank is much too small, I know, it's a 0.5 gallon. (*prepares to be yelled at*) But I change the water twice weekly and it's got a heater.
– I use Nutrafin Betta Plus water conditioner, which is tropical almond leaf extract, apparently.
– It's freshwater, and has been set up for about ten days. Up until now, my fish had been happy and healthy!
– There's only the one fish.
– The tank temperature right now is 82F.
– No plants any more, will go buy more soon. (Took them out a couple of days ago as they were getting manky/gross.)
– No filter, as per recommendation, just frequent water changes.
– Natural sunlight rarely, generally it's lit indirectly by room lights, not very bright and quite far away. It's only lit for maybe 8 or 9 hours a day, the rest of the time it's very dim or dark.
– Last water change was yesterday morning, full change, though I let temperature get to exactly the same as it was before.
– I alternate between betta flakes and pellets. Once a day, as much as he can eat in a minute or so, and I remove the rest. Normally around 4 or 5 pellets or three flakes.
– No treatment so far, no other symptoms other than these strange white markings and he seems a bit more agitated lately.