Ask a mackerel buyer in Japan what they need and the first number you get will be a fat percentage, not a weight grade. Ask a supplier for the fat percentage of “Norwegian mackerel” and any answer that arrives without a lot number attached is a marketing figure.
Both of those facts follow from the same thing: fat in mackerel is a property of the fish at the moment it was caught, not of the species.
What fat does to the product
Fat content drives most of what a processor cares about:
- Texture and mouthfeel. Higher fat gives a softer, richer flesh.
- Smoking behaviour. Fat carries smoke compounds and affects yield and finish.
- Grilling performance. Higher-fat fish behaves differently over heat than lean fish.
- Oxidation risk. More fat means more surface fat to protect, which raises the importance of glaze and of cold-chain discipline.
- Canning and marinating outcomes. Both are sensitive to fat level.
A lean mackerel and a fat mackerel of identical weight are not substitutes for each other in most industrial processes.
Why it moves
Mackerel feed through the summer and build fat reserves ahead of winter. The Norwegian fishery is concentrated in late summer and autumn, and fat content is typically at its highest toward the end of that window.
But the seasonal pattern is a tendency, not a guarantee. Fat also varies between schools caught days apart, with feeding conditions in a given year, and with the size of the fish. This is why an analysed figure for the specific lot is the only figure worth contracting on.
How to buy on it
Three lines in the enquiry:
State analysed fat percentage for the offered lot. State catch date and catch area for the same lot. Offer to remain valid against that lot only.
That last line matters. A fat figure that applies to a lot which has been sold by the time you accept is not information; it is decoration.
Reading an offer
When you receive a mackerel offer, the useful fields in order of importance are:
- Catch date
- Analysed fat percentage
- Weight grade and the grading system it comes from
- Sea frozen or shore frozen
- Pack style — jumble or hand laid
- Glaze percentage and net weight basis
Weight grade, the field most offers lead with, is third.
What we will not publish
We do not publish a fat percentage for mackerel as a species figure on this site, and we would suggest treating any supplier who does with some caution. The number changes. Ours comes with the lot.