1. Remove any skin and bones from fish.
2. Flake the flesh.
3. Mash out any lumps in the potato.
4. Separate the yolk and white of 1 egg.
5. Combine thoroughly fish, potato, egg yolk, seasonings and tomato paste (if used). The mixture should be stiff enough to mold; add extra potato or a tablespoon of flour if needed.
6. Roll mixture into small balls.
7. Beat remaining egg and egg white until liquid.
8. Dip in the fishballs, then roll them in crumbs.
9. Allow to stand for 1 hour.
10. Heat oil in a deep pan, and fry fishballs, a few at a time, until surface is crisp and brown.
11. Scoop out with a slotted spoon and drain on soft kitchen paper.
12. Serve hot or cold on cocktail picks.