Insert the stainless steel inner pot into the Instant Pot and add the water. Close and lock the Instant Pot® lid, making sure the steam release handle is turned to Sealing. Press Soup/Broth and set the time to 4 Minutes.
When the time is up, release the steam (by turning the handle). Once all the pressure is released, open the lid, add the fish head, backbone, and salt; wait for it to come to a boil again (without covering the pot).
Then add onion, ginger, celery, coriander stems. Press Soup/Broth and set the time to 10 Minutes.
When the time is up, release the steam (by turning the handle). Once all the pressure is released, open the lid, add fish, onion, and coriander. Let stand for 2 Minutes and check for salt.
Serve chilcano fish broth with toasted corn, lemon drop pepper and chopped coriander.