1) Place cod in a pot and fill with cold water, covering cod completely. Soak at least 12 hours, at room temperature. Remove from water and rinse.
2) Heat oil to 185 degrees C in a deep pot until it comes about 5cms up the side of the pan.
3) In a medium saute pan, over medium heat, add oil and saute onions, celery, and garlic, until vegetables soften, about 5 minutes. Remove mixture to a bowl and let cool. Add cayenne, spring onions, coriander, lime zest and juice, flour, baking powder, milk and egg. Mix together well.
4) With a fork, flake the cod, being sure to remove the skin. Add the cod to the batter.
5) Using an ice cream scoop, scoop up fritter batter and place into preheated oil. (Fritters should measure about 3cms in diameter.) Work in batches. Don't add more than six at a time. Cook until fritters are golden and cooked through, about 6 to 8 minutes. Remove to a paper towel lined plate to drain.