"At all locations, tritium concentrations were found to be below the detection limit (detection limit: approximately 10 becquerel/liter)."

https://www.meti.go.jp/english/press/2023/0825_003.html

"The Fisheries Agency announced on the 26th that the radioactive material tritium was not detected in a survey of fish in the surrounding sea area following the release of treated water from the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station into the ocean"

https://www.yomiuri.co.jp/national/20230826-OYT1T50207/

This is clearly a nothingburger. Articles complaining about it (without considering the background radioactivity in the ocean) reveal more about the authors than they do about the subject.