Here's why:
* Long Tapered Body: Most fish have a streamlined, elongated body shape that helps them move efficiently through water.
* Tail Fin on Each Side: Fish have a caudal fin (tail fin) that is typically positioned at the end of their body and helps them propel themselves through the water.
However, other possibilities include:
* Eel: Eels have a very long, snake-like body and a small, fin-like tail.
* Dolphin: Dolphins have a streamlined body shape and a tail fin, but they are mammals.
* Shark: Some sharks have a more elongated body shape and a tail fin with a large upper lobe.
To give you a more precise answer, I would need more information about the animal's size, color, and any other distinguishing features.