Pleco catfish appears to be losing slime layer?

My juvenile catfish has looked the same since I got her 3 months ago, and this is the first noticeable change in appearance.

No noticable changes in attitude or behavior, no recent diet changes, water changed recently and was in good health to the best of my knowledge. Tankmates are another pleco, guppies and an angel fish.

This is my first time keeping pleco and I'm very fond of her, can anybody let me know if this is something to be worried about?