Heavy metals for RFO are tested periodically throughout the year.
Rosita tests Ratfish Liver Oil so infrequent because the number is zero when tested.
The reason for this is that Ratfish is a bottom dweller, and heavy metals tend to accumulate in the fillet and not the liver. This holds true for Cod Liver Oil as well, the liver does not contain heavy metals but because the cod has different habits, it is more susceptible to high toxins.
Fishing is a big business in Norway, their government is big on sustainability for all fish and are very strict with testing.
The other testing for RFO is done on every batch. Heavy metals are not a concern for Ratfish. Dioxins are the concern for bottom-dwelling fish and Rosita test well under the recommended levels.