Concept:Compost manure enriches pond water with nutrients, which increases phytoplankton growth and improves fish production.
Explanation:When compost manure is added to a fish pond, it breaks down and releases dissolved nutrients into the water.
These nutrients, such as nitrogen and phosphorus, support the growth of phytoplankton, which are microscopic primary producers.
Phytoplankton serve as a major food source for fish.
As the phytoplankton population rises, more food becomes available for the fish.
This leads to better feeding, growth, and survival of fish in the pond.
Therefore, fertilizing a fish pond with compost manure causes both the phytoplankton population and the fish yield to increase together.
Answer:D. Phytoplankton population increases as fish yield increases.