Do all fish have a "tail"?

Question

My dear daughter believes that there are some fish without any tails. I believe that to be called a fish, it must have a tail.

Who is right? Ice-cream is riding on this!

Thanks,

Cris

Answer 1

Well, that depends on your definition of "tail".

If a tail is defined as an extension of the vertebrae (or notochord) behind the anus or cloaca, then most fish do have a tail.

There are some few exceptions, for example the ocean sunfish ( http://www.oceanlight.com/html/mola_mola.html). These fish don't have a caudal fin with normal tail vertebrae; it is replaced by modified caudal elements. This condition is known as "gephyrocercal" (http://www.briancoad.com/Dictionary/DicPics/gephyrocercal.htm).

If, however, you're thinking of a typical caudal fin, there are many fishes without them, such as eels and other anguilliform species. However, they usually do have caudal vertebrae (it is the membrane that they lack).

Answer 2

It depends on just what you mean by a "tail". All fish obviously have a posterior end that could be called their "tail", but not all fish have a tail FIN that extends upward and downward at the end of the tail. For example, eels and ratfish. And of course rays.

Here's a ratfish. You decide if it has what fits your definition of a "tail":

http://www.parcdistributors.net/chimera.jpg

.

Answer 3

a tail fin derrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr