Your answer would likely be "fish" - but there are several ways of thinking about the question!
Biologically, the fish is the only one of the four without a hard shell.
By language, fish is the only one without the letter "L".
There are probably other answers too - these were just off the top of my head, but the biological answer is the most obvious and likely one.
Cowboys loved a colorful phrase! This meant an eccentric person. A hermit would be considered an odd fish.
Eat the even numbered fish.
An odd or eccentric person.
James Kennedy.
Odd one is: Fish (can't live outside water!)Frog, Tortoise, Crab - can survive both in water as well as on land
Cockles look like two ruffles potato chips placed together in the shape of a clam. (I know this sounds odd, but it is the most accurate description I can come up with). cockles almost look like a clam but it can be pretty!!!!!!!you can almost tell the difference between them.
guitar
The barreleye fish is also known as the spookfish. This odd looking fish can get up to 6 inches (15 centimeters) long.
It's an odd-looking, Saltwater Fish that is used by McDonalds in theie Fillet-o-Fish Sandwich. It's been in the news because they are being over-fished
an eel is a vertebrates all fish no matter how odd are vertebrates
The dolphin is a mammal.
Oh, dude, the odd one out is Robin because it's not a fish! Like, trout, herring, cod, and pike are all types of fish, but Robin is just chilling there, probably wondering how it ended up in the seafood section.