Fisheyes are small round spots that appear to repel a paint or varnish from an area, even if paint or varnish is reapplied to the area. They can range from being less than 1/8" to over 1" or bigger. The cause of these spots is purely surface contamination, commonly due to poor surface prep, or possibly a surface contaminant that was not removed prior to sanding the substrate in preparation to being top coated.
Prevention is the best way to handle getting fisheyes. Always take extreme care and follow all surface preparation, without cutting corners. Do not substitute surface preparation solvents.
Two-component paints and varnishes are more sensitive than 1-component products when it comes to fisheyes. The only way to alleviate fisheyes is to remove the coating from the affected area, ensure better care when performing the surface preparation, then reapply the coating.