Classification hinges on species identity. Bluefin species (Thunnus thynnus, Thunnus orientalis, Thunnus maccoyii) have dedicated HTS lines. All other Thunnus species — including yellowfin, bigeye, albacore, and longtail — fall under 0303490200 when frozen in whole or dressed form. Species must be identified by scientific name on commercial invoices and catch documentation; a generic description of 'tuna' is insufficient for proper classification.

Ecuador operates under IATTC management for the Eastern Pacific Ocean. Shipments of yellowfin or bigeye tuna from Ecuador should be accompanied by IATTC-consistent catch documentation, and NOAA SIMP requires harvest event data — including vessel name, flag, gear type, and fishing area — submitted at entry. For bigeye specifically, importers should verify that the catch falls within Ecuador's IATTC bigeye allocation, as overage can trigger trade-measure scrutiny.