Clean the fish and remove bones.
Take the fish in a large bowl and add ginger-garlic paste, salt, 4 tbsp vinegar, pepper powder and mix well and keep aside for 30 minutes.
Once the the fish has been marinated, heat oil in a pot and deep fry the marinated fish pieces.
Once it is over, into the same oil add mustard seeds and allow it to splutter.
Then add chopped ginger and garlic and allow it to be light brown. Now slow down the flame and add chilly powder and mix it well and allow to be heated.
Add remaining vinegar into it. Allow the vinegar to be boiled well and add salt, turmeric powder and asafoetida powder.
Stir the mixture well and add the fried fish into it and mix well. Add curry leaves.
Check whether salt is enough. Now the pickle is ready and store in dry bottle after cooling.