0303.54.00.00 - Mackerel (Scomber scombrus, Scomber australasicus, Scomber japonicus)

This HTS classification covers frozen mackerel, specifically the species *Scomber scombrus*, *Scomber australasicus*, and *Scomber japonicus*. These are whole, unprocessed fish intended for consumption or further processing, distinguished from their fillets and other fish meat classifications under heading 0304. The key classification criterion here is the frozen state of the whole fish.

Within the broader category of frozen fish excluding fillets, this subheading is distinct from its siblings by its precise enumeration of mackerel species. For example, it differs from 0303.51.00.00 which specifically covers herrings, and from 0303.53.00.00 which includes sardines, sardinella, and sprats. Similarly, it is differentiated from 0303.55.00.00 which pertains to jack and horse mackerel.

As a leaf node within the HTS, 0303.54.00.00 does not have further subcategories. Classification at this level is definitive for frozen mackerel as described. Importers and exporters should ensure that the goods precisely match the listed scientific and common names to avoid misclassification.