Afish is resting in a shady part of the water, protected by surrounding rocks. the fish suddenly moves out into an open area that is sunny and closer to the surface of the water.

what is most likely the reason the fish moved?

to increase its body temperature
to slow down blood circulation
to obtain oxygen
to take in extra carbon dioxide

I think the answer is to increase its body temperature.

to increase its body temperature

Explanation:

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.