Answer: D. cellular respiration
Step-by-step explanation:
Cellular respiration is a process which involves the break down of glucose molecules into water and carbon dioxide present in the food so as to release energy in the body in the form of ATP and also releases wastes.
The fish being a consumer in the food chain will eat algae as a food source. The cellular respiration process in fish will break down the glucose molecules in the algal food and will provide energy to the fish.