Prepare the Blender: Set up a high-powered blender.
Combine Ingredients: Add the lime juice, fish, fish stock, onion, garlic, celery, ginger, cilantro stems, and ají limo paste into the blender.
Blend: Process the mixture until completely liquefied, approximately 5 minutes.
Season and Chill: Add the salt and a few ice cubes to the blender, then blend until thoroughly combined, about 30–60 seconds more.
Strain: Pour the mixture through a fine mesh strainer into a large bowl or measuring cup, discarding any solids.
Serve or Store: Use immediately as a marinade for ceviche or as a standalone beverage. Alternatively, cover and refrigerate for up to one day, or freeze for up to one month.