Peace be upon you. According to Grand Ayatollah Khamenei and Grand Ayatollah Sistani (may Allah protect them): There are two conditions for the permissibility of eating fish: First, it must have scales according to common understanding. Second, it must be caught alive by the fisherman or die in the fishing net or pen. It is not a condition for the fisherman to be Muslim, nor is it necessary to mention the name of Allah during the slaughtering of the fish. If a non-Muslim catches the fish and takes it out of the water alive, or it dies in the net or pen, and it has scales, it is permissible to eat it. If one doubts whether this fish has scales or not: Grand Ayatollah Khamenei (may Allah protect him) rules it permissible. Grand Ayatollah Sistani (may Allah protect him) rules it as impermissible. May you be successful in all good deeds.