Japanese researchers use subtle smell to determine freshness of fish

According to The Asahi Shimbun, an odor-sniffing machine that shows the freshness of fish is expected to further the popularity of sushi and sashimi overseas.
The portable device detects a smell associated with early decomposition. The aroma is a subtle one, and not the stinky ammonia that rotten fish is known for.
The project aims to establish technology to “measure freshness quickly, on site, and in a non-destructive manner,” said Toshio Ito, a senior researcher at the National Institute of Advanced Industrial Science and Technology, better known as AIST.
The device was created by scientists from AIST and the Hokkaido Industrial Technology Center.

https://www.asahi.com/ajw/articles/15033378