How sunlight regulates the productivity of algae and the number of catfish in a pool.

Algae produces food and catfish also needs warm water.

Explanation:

Sunlight regulates the productivity of algae and the number of catfish in a pool because algae produces food in the presence of sunlight during the process of photosynthesis. If algae produces more food, so more food is available for the catfish and as a result the population of catfish increases. If no sunlight occur on the pool the algae is unable to produce food and the population of catfish decreases. Sunlight increases the temperature of water which makes environment suitable for the catfish because catfish needs slightly warm water for its growth. So we can say that sunlight has a great affect on algae and catfish.