This process is called Cellular respiration. Cells break down glucose to make ATP (adenosine triphosphate) Here is the formula for cellular respiration, C6H12O6 + 6O2 - 6CO2 + 6H2O + ATP
The first one is glucose, then oxygen. These make carbon dioxide, water and ATP. Hope this helps :)
The only thing I can think of is how many gill flaps(of a fish), how often or speed of movement, and how fast it eats? I did a lab with a goldfish studying metabolism and counted the amount of gill flaps every 60 seconds with different temperature water. Hope it helps!
