I cannot watch the actual video at the moment, but given this is in Prick News, I expect what was actually said to be distorted beyond belief. Kind of like when it was claimed that one of the speakers had said all trans people were parasites, which was untrue also.
I have actually heard of this transfish stuff before though, on another site, months and months ago. Apparently (though this may have been clickbaity also) its because of how carelessly some dispose of medications, mainly the pill. And its 'changing the sex' of some fish. Or something. Vaguely remember it. Not sure if its possible or not though.