Houses have been built around a small retention pond, increasing the fertilizer runoff into the pond. This has led to algal blooms in the pond which periodically reduce the amount of dissolved oxygen available in the water. What will be the most likely long-term effect on the fish population living in the pond if the situation with the fertilizer does not change?

The fish population will grow as more offspring are born that can take advantage of the new conditions.
The population will be replaced by a different species of fish that consumes algae for food.
The fish population will learn to survive with less oxygen and more algae in the water.
The population will evolve, leaving only those genetically equipped to deal with low oxygen levels.