In a large stockpot over medium high heat, heat the olive oil.
Add the onions, carrots and celery and cook, stirring, until soft and slightly browned, 10 minutes.
Add the juice to deglaze the pan.
Add the fish, mushrooms, bay leaves, star anise, thyme, konbu, cilantro and water, ensuring the ingredients are covered by 1 to 2 inches.
Bring to a simmer, then lower the heat. Do not allow the liquid to boil. If you have an instant-read thermometer, lower the heat when the temperature reaches about 80 degrees C. Simmer for 1 hour.1
Use a double/ultra fine mesh strainer, if available. If not, line your strainer with single-layer paper towels or a cheesecloth.
After the stock has simmered for max 1 hour, turn the heat to the lowest setting possible. Ladle the liquid through the prepared strainer.
Use as desired. The stock is at best used on the same day, otherwise it will keep for up to 1 week in the fridge or 6 months in the freezer.