In north east England the water authority used a trout in a tank with the mains water flowing through.  The fish's vital signs were monitored electronically.  Came across this in 1999 while doing millennium compliance testing.,(reply>), @Akshay Anand are you for eel? It’s not a crime to make carp jokes! 😤,(reply>), Also in Prague they have similar setup.,(reply>), @Lucina In some vital systems it is a valid concern. It's just that there was enough testing and modernization in those systems that Y2K didn't really do much harm.,(reply>), @Lucina I can see you were fishing for some laughs but no one took the bait.,(reply>), Fish Monitors were also used in a Chemical Plant in Austria to Test the used Cooling Water.