How to Identify a Good Fish and Reject a Bad One
Take the fish and stick your nose in the hole where the head was. If you wish that you hadn’t done that, send the fish back. Run your finger along the blood line inside the belly, head to tail, and smell it. If you smell anything, send it back.
If your fish arrives with a head, examine the eye. The Japanese will tell you to judge freshness by the convexity of the ball. But the Japanese would never buy a headless fish, and we would. If the eye is round rejoice and touch the skin: A fish just from the ocean will ooze a slime clean like egg white; but a fresh fish can lack this if it is packed in abrasive crushed ice. If it is slimy rejoice twice and proceed.
If your fish is of the fatty spawning variety and gutted, pinch the belly between your thumb and forefinger. It should be thick, about an inch think, never less than a half, and it should be firm, too firm to roll back and forth to the left and right. It should feel substantial, rubbery and fleshy, like a big piece of string cheese. And the same glossy white color. A fish that passes the caliper test was healthy when it was caught, just beginning its fasting fight upriver. A fish that fails was at the end of its life and starving when it was caught. The belly fat is gone and so is the flavor. Send the fish back.
If your fish passes the belly fat test, put your finger at the creature’s tale. Run this finger along the belly towards the gills. Now look at your finger. If it is clean, your fish is fresh; it was recently caught; it has not been out of the water very long. If on the other hand, you see more than one or two scales, or worse, spy them jumping off of your fish’s belly and are now covered, face, arms, and apron, in glittering scaly sequins, your fish is old. Dead too long. No thank you.