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METROLOGY IN THE SERVICE OF KEEPING FISH ON OUR PLATE SAFE

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When we buy fish or fish products, we expect them to be fresh, safe, and fit for consumption. To achieve this, reliable temperature measurement is essential — from storage temperature to the conditions during laboratory analysis.

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Ensuring the safety and quality of fish begins already on the boat. Immediately after being caught, fish must be chilled to a temperature close to 0 °C, and during storage and transport the temperature must not exceed +2 °C. If these conditions are not met, bacteria develop rapidly and compounds such as histamine can form, potentially causing poisoning. This is why fish markets, cold stores and distributors must use calibrated thermometers to ensure reliable measurements.

(Visual 1: Measurement of fish temperature at a marketplace / Source: ChatGPT)

 

(Visual 2a & 2b: Histamine determination in fish / Source: Eurofins Croatiakontrola d.o.o.)

 

In the laboratory, the presence of harmful substances is examined. Mercury is the most commonly monitored contaminant, especially in large predatory fish such as tuna or swordfish. To obtain reliable results, temperature control is essential at two stages:

 

  • Sample storage: samples are kept at 0–4 °C or frozen at –20 °C until they reach the laboratory, to prevent changes in the tissue.
  • Analysis: in instruments such as the atomic absorption spectrometer (AAS), temperature must be precisely set in the atomiser and during the sample digestion process. If the temperature is too high, part of the analyte may be lost — the result is an artificially low mercury value. If the temperature is too low, tissue digestion is incomplete, meaning not all mercury is released from the sample — again yielding an incorrect, underestimated result.

 

(Visual 3: Temperature and measurement chain “from boat to plate” / Source: ChatGPT)

 

These falsely low results are particularly dangerous because they can lead to contaminated fish entering the market, containing too much mercury to be safe for consumers. This is precisely why metrology — through calibrated instruments and accredited laboratories — plays a crucial role in protecting public health.