All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is permissible to eat fish on all days; we did not find any evidence suggesting that it is a Sunnah to eat fish or abstain from eating it on a specific day or a particular time. This might be part of people's customs and habits.
Allaah knows best.