Measuring Fish with Torrymeter

Changes to Fish Freshness Meter From Serial No. 8301

Further research and extensive field use of the instrument on many varieties of fish have revealed that the temperature compensation device incorporated into the original instrument can be misleading.

This temperature correction is accurate only for cod, and it was wrongly assumed that other species behave in the same way as cod. It has been decided that it would be in the best interests of the majority of users for the thermistor temperature compensator to be removed. This does not mean that the instrument cannot be used at temperatures other than 0°C, but rather that the user must determine the temperature coefficient of the species being tested, and apply a correction to the reading.

To avoid the need to apply a correction, the instrument should be used only on fish at an even temperature of 0°C, since this gives a completely consistent and stable reference temperature. An instrument with the temperature compensator fitted (prior to serial no. 8301), should be ‘cooled down’ as described on page 9, paragraph 4 in the handbook. Do not take readings on fish that have been left exposed to direct sunlight, especially in hot countries.

Initial research and trial recordings should only be carried out on fish stored in crushed ice, these experiments can be repeated easily if a malfunction of the meter is suspected.

The ‘single shot’ mode is not recommended for measuring freshness of individual fish within a batch because readings will vary. This fish-to-fish variation is caused by 2 factors:

  • Variation in intrinsic freshness among individual fish;
  • Variation of meter readings among fish of the freshness.