Thanks to /u/DericStrider for the mention.

In the post he linked, we sort of explain how the harbor wasn't really affected by the tea in any measurable way. Likewise, any fish that would have been there would have likely been unaffected, especially since they couldn't even accidentally eat the tea since it was properly packed away in containers.

Please let me know if you have any follow up questions!

Sorry if this doesn't properly answer the question of historical reports (please delete if so) but I believe these answers in this thread would explain why there might not be any reports of fish dieing https://www.reddit.com/r/AskHistorians/comments/78698b/did_the_boston_tea_party_turn_the_water_in_the/?utm_content=title&utm_medium=front&utm_source=reddit&utm_name=AskHistorian

Commentators /u/uncovered-history and /u/IAmDotorg explain that the water was too cold, too large a body of water and the tea was packed inside chests to turn the bay into tea.

I would guess the fish would not have been affected much as the tea chests rotted and the tea floated away or settled on sea bed.