Indonesian tuna (gohu ikan) in spicy and tangy citrus

This Indonesian tuna recipe in spicy and tangy citrus comes from Petty Pandean-Elliot's book The Indonesian Table (£24.95, Phaidon Press).

Petty says: "The Manado word gohu translates to ‘pickled’ in specific dishes such as gohu papaya, where ripe papaya is pickled for at least 24 hours. But in this case it is used to describe a quick, spicy and tangy marination of tuna. I first learned of this dish on a visit to a fishing village near Likupang, a hot Indonesian tourist destination in my hometown of Manado. As the story goes, local fishermen would go out to sea with pouches of fresh chillies, shallots, calamansi and salt. When hunger struck, a few freshly caught fish were filleted on the spot and combined with the ingredients in the small bags. Quality is paramount, so you must use high-quality fish. Ask a trusted fish supplier for sashimi-grade tuna."