During the refrigerated storage of fresh fish (0°C to 4°C):

It is crucial to maintain the relative humidity at around 90% RH to slow down the evaporation of moisture from the fish, preserve the firmness and tenderness of the flesh, and minimize damage caused by condensation from melting ice crystals.

• Dehydration Risk:
  If humidity drops below 85% RH, moisture rapidly escapes from the fish surface, leading to shrinkage and surface cracking, which can cause a weight loss of 2%–4%.

• Microbial Risk:
  When humidity exceeds 95% RH, condensation forms within the storage environment, creating an ideal breeding ground for bacteria and mold. This can lead to the development of a slimy layer and unpleasant odors.

During frozen storage of aquatic products (≤ –18°C):

Despite the extremely low temperatures, it is still essential to maintain a relatively high humidity level (around 85%–90% RH) to prevent “freezer burn” or frost damage on the surface of the fish caused by excessive temperature differences, and to reduce tissue damage from freeze-thaw cycles.

• Frost Prevention Design:
  Maintaining a temperature difference of about 5°C between the evaporator and the storage room helps achieve an internal environment of 85%–90% RH. Special dual-system designs, such as jacketed cold rooms, can even reach humidity levels above 98% RH.

• Efficient Freezing:
  During IQF (Individual Quick Freezing) processes (–30°C to –40°C), controlling humidity between 40%–60% RH strikes a balance between rapid freezing and slight moisture retention, helping to lower the rate of cell wall rupture.

• 
  

• 

Conclusion

The humidity requirements for aquatic product cold storage are extremely stringent:

• During fresh storage, the relative humidity should be maintained at around 90% RH.

• During frozen storage, it should be kept between 85%–90% RH.

By implementing techniques such as pre-dehumidification, frost-free constant humidity systems, and precise humidity monitoring, cold storage facilities can effectively prevent dehydration, frost damage, and microbial contamination.
This ensures that aquatic products remain in optimal condition from entry to exit, extends shelf life and edible quality, and simultaneously reduces energy consumption and operational costs.
High-standard humidity management has become an indispensable core element in modern cold storage operations.