Mackerel grading looks simple — weight bands, in grams — and it is, right up to the point where two suppliers use overlapping ladders and nobody says which one they are on.
The core ladder
Most Norwegian mackerel is traded on four bands:
| Grade | Imperial |
|---|---|
| 300–400 g | 10.6–14.1 oz |
| 400–500 g | 14.1–17.6 oz |
| 500–600 g | 17.6–21.2 oz |
| 600 g+ | 21.2 oz+ |
The weight is gross weight per fish, whole round, before glazing.
The extended bands
Specific destination programmes use additional bands: 150–250 g, 200–400 g, 250–400 g, 300–500 g and 400–600 g among them. These overlap the core ladder rather than extending it. A fish at 420 g sits in the core 400–500 g band and simultaneously in the extended 400–600 g band and the extended 200–400 g band’s neighbour.
That overlap is fine as long as the contract names the system. It is not fine when one party assumes the core ladder and the other is grading to an extended one.
Write the system, then the band. For example: “core grading, 400–500 g” or “extended grading, 300–500 g”.
The four fields beside the grade
A weight band alone does not define a mackerel purchase. Four further fields do most of the work:
Catch date. Establishes where in the season the fish sits, and with it the likely fat level and the time already spent in frozen storage.
Analysed fat percentage. For the specific lot. See why fat percentage matters.
Freezing location. Sea frozen or shore frozen. Both are normal; they are different products.
Pack style. Jumble packed or hand laid. Hand-laid fish arrives straight and presentable and costs more to pack. Jumble packing is cheaper and entirely correct for a processing line. Choosing the wrong one wastes money in one direction or the other.
Add the glaze percentage and the net weight basis and the specification is complete.
Presentations
Beyond whole round, mackerel is traded as fillet and as butterfly (flap) — head off, backbone removed, the two fillets still joined. Butterfly is common in grilling markets. Each presentation has its own yield relationship to the whole-round weight, so a grade band does not carry across from one to another.
A complete line
Atlantic mackerel (Scomber scombrus), whole round, frozen at sea, core grading 400–500 g, hand laid, glaze 8 % maximum, price per kg net of glaze, catch date and analysed fat to be stated per lot.