When fish meat goes bad, it can be described in several ways in English. Here are some common phrases:

has gone offor has spoiled: This is a general term for when food is no longer fresh and has a bad smell or taste. For example, "The fish meat in the fridge has gone off."

has turnedor has gone rancid: These terms are often used to describe a specific type of spoilage that occurs when fats in the food degrade, giving it a rancid flavor. For instance, "The fish oil has turned rancid."

has expired: This term is specifically used for food that has passed its recommended shelf life and is no longer safe to eat. For example, "The fish meat has expired and should not be consumed."

is bad: This is a simple and direct way to say that the fish meat is no longer good to use. For example, "The fish meat is bad； don't eat it."

Using these phrases, you can accurately describe the condition of fish meat when it has变质（gone bad）.