Swordfish is one of the largest species harvested commercially, with some individual fish topping 1,000 pounds. In practice, those you'll find at the fishmonger usually average 50 to 300 pounds, which is still a large fish. Swordfish has a distinctively firm, meaty texture and mild flavor that appeal even to those who don't like fish. Although there's no formal grading process for swordfish, there are several quality indicators to be aware of.
Although there is no official standard in the U.S. for grading swordfish, the fish's marketers have evolved a system of their own to indicate the highest quality product. This is labeled as "sashimi grade" swordfish, since sashimi requires fish of the very best quality. Sashimi grade swordfish can only be line caught, and it's processed immediately on the fishing vessel. The freshly butchered fish is flash-frozen immediately at temperatures of -76 F to preserve its quality. Sashimi-grade swordfish is also selected for visual appeal, with only the whitest and most perfectly cut portions getting this designation.
Swordfish that doesn't meet the exacting standards of sashimi grade is sold, logically, as non-sashimi grade. This grade need not be line caught, and its color might not be as purely, perfectly white as that of a sashimi-grade fish. Non-sashimi grade swordfish might also include individual portions which were of sashimi quality, but weren't cut neatly enough to fetch top dollar. Swordfish processed on land or on vessels lacking the ability to blast-freeze at -76 F, also can't be sashimi grade. This makes non-sashimi grade swordfish more variable, though the best is still very good swordfish.
Aside from sashimi or non-sashimi grading, there are several quality indicators for savvy shoppers. Swordfish includes both white and dark meat, and their color is a telling indicator of freshness. The white meat should be very white and clean-looking, and the dark meat or bloodline, as it's called, should be red. In older swordfish, the white meat will begin to develop a grey tinge and the bloodline will turn from red to brown, and eventually grey-brown. Smell is important, too. Fresh swordfish should have very little smell, aside from a faint hint of fresh seawater. If it smells fishy, it's old.
As a large and dominant predator, swordfish live at the top of the aquatic food chain. This means that they have a tendency to concentrate mercury in their tissues, a potential health issue. The elderly, pregnant and nursing women and those with compromised immune systems should avoid swordfish. Healthy seafood lovers should enjoy swordfish in moderation--no more than twice a month--to limit their exposure. Swordfish must be kept perfectly cold during processing, otherwise it's prone to cause scombroid poisoning, also known as scombrotoxin or histamine poisoning. Although seldom life-threatening, this illness is thoroughly unpleasant.