I have used nail polish with moderate success. For black scales, make sure it has no glitter in it, you'd be surprized how hard it is to find nail polish that is just plain black.

Fill the gaps with many thin coats. Let cure a day or so. Sand flush and polish. Presto, no more bites.

Worth noting, however, is that nail polish doesn't cure super hard. You can dent it with a fingerail. This helps, since scales need to flex and the repair will be more robust, but don't expect it to be bulletproof.