You are given a sentence and your task is to generate another sentence that supports the given input.

Let me give you an example: In spite of this reduced heat input, the surface temperature of Venus is higher than that of the Earth.
The answer to this example can be: Venus has a warmer average surface temperature than earth.
Here is why: Output statement supports the input statement's claim about the temperatures of Venus being higher than the earth.

OK. solve this:
Fins are used by fish to move through the water but also to  steer, stop and maintain their position, the latter in conjunction with  the swim bladder.
Answer:
Fish use some of their fins to propel themselves through the water and some of their fins to steer.