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How does refrigerated seawater cool harvested fish?

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fish on a conveyor belt — fish processing Fish on a conveyor belt entering a processing plant, Newfoundland, Canada.

Refrigerated seawater is used as a low-temperature environment to chill harvested fish immediately, maintaining temperatures between 2 and −2 °C (36 and 28 °F). This process is essential for slowing the growth of microorganisms and inhibiting enzyme activity, which prevents the rapid structural degradation to which fish are susceptible.12

Compared to traditional ice cooling, refrigerated seawater offers the advantage of causing less bruising and structural damage to the fish carcasses. However, because fish held in this medium absorb salt, the duration of storage must be limited for products intended for the fresh or frozen market. When the fish is destined for canning or smoking, processors adjust the salt levels in those subsequent stages to compensate for the absorption that occurred during the chilling process.2