There are several common ways of harvesting fish from the wild, none of them ideal. In the most controlled and least efficient method, a few fishermen catch a few fish, ice them immediately, and deliver them to shore within hours. This method can produce very fresh and high-quality fish – if they are caught quickly with minimal struggle, expertly killed and cleaned, quickly and thoroughly iced, and promptly delivered to market. But if the fish are exhausted, processing is less than ideal, or cold storage is interrupted, qualify will suffer.

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By contrast to the logistical challenges posed by fishing, consider the care with which salmon are harvested in the best aquaculture operations. First, the fish are starved for seven to ten days to reduce the levels of bacteria and digestive enzymes in the gut that may otherwise accelerate spoilage. The fish are anesthetized in chilled water saturated with carbon dioxide, then killed either with a blow to the head or by bleeding with a cut through the blood vessels of the gill and tail.  Because the blood contains both enzymes and reactive hemoglobin iron, bleeding improves the fish’s flavor, texture, color and market life. Workers then clean the fish while it’s still cold, and may wrap it in plastic to protect it from direct contact with ice or air.

- Harold McGee, On Food and Cooking