This artifact is most noticeable in MPEG and DV25 compressed video, but can be found in all DCT based codecs, including JPEG still images. Areas of high contrast, such as text on top of solid-colored backgrounds will exhibit mosquito noise (i.e., on screen menus captured in DV25). Outside of noise around high contrast text, it may be most apparent in bright footage with very fine detail and strong horizontal or diagonal object arrangement.

Can it be fixed?

No, Mosquito Noise cannot be remedied.