There are many misconceptions about what a vegetarian diet is and isn't. While there are plenty of gray areas when it comes to what individual vegetarians eat, eating the flesh of any animal is never considered to be vegetarian. That includes the flesh of dead fish.
To make it absolutely clear: fish is not vegetarian. Please do not cook fish for your vegetarian friends and family members. If you work at a restaurant, please do not offer to bring the seafood special to a customer who says they are vegetarian.
The simple fact is that fish are animals that live in the water. Fish and seafood of any kind—just like the meat of other animals—is not vegetarian. Fish is not vegetarian, shrimp is not vegetarian, lobster and crab are not vegetarian, and eating any kind of animal which lives in the sea, lake, or river is not vegetarian.
Can I Eat Fish If I'm Vegetarian?
Being a vegetarian is a choice. While you can eat whatever you want—from burgers to chicken to fish to dairy—if you choose to be vegetarian, you have decided to avoid those foods.
There are many reasons why people choose to be vegetarians, including animal welfare, the environment, sustainability, and global warming. Yours may be different than someone else's or you may share similar convictions with the majority of vegetarians.
Many vegetarians simply do not want to eat meat or fish. It's a choice they've made and they don't miss it at all—there are plenty of other things in the world to eat. Some people also choose to go the vegan route and avoid any foods made with any type of animal product, including ingredients like dairy and gelatin.
If you're a vegetarian who wants to eat fish, you may want to consider why you want to eat fish and why you want to be a vegetarian. Which list of reasons is more important to you? It's a personal decision that everyone must come to on their own.
Still confused about whether or not vegetarians can eat fish? Consider this. A triangle, by definition, has three sides. No one, no matter how hard they try, can possibly make a 4-sided triangle.
In the same way that you cannot make a 4-sided triangle, you cannot be a meat-eating vegetarian by a simple definition of terms. Also, you cannot be a fish-eating vegetarian for the simple fact that fish is not vegetarian. It should go without saying that fish is also not vegan.
And that is what fish-eating vegetarians and four-sided triangles have in common: they cannot and do not logically exist. Period.
"I'm a Vegetarian, But..."
There are, indeed, many people who say "I'm a vegetarian, but....". They may say, "I'm a vegetarian but I eat fish." Or chicken. Or bacon. Or whatever. None of their personal exceptions changes the fact that a vegetarian, by definition, does not eat fish, or chicken, or bacon.
You can, however, be a pescetarian and enjoy fish and seafood. You can also be a flexitarian, which isn't really a thing at all but is sometimes used to describe a semi-vegetarian. You may also simply prefer eating vegetarian meals the majority of the time. However, with any of these, you would not be considered a true vegetarian unless you refrain from eating meat and fish altogether.