What would most likely happen to fish in a pond with low levels of dissolved oxygen?

• A. Fish would switch to photosynthesis to obtain energy.
• B. Fish populations would increase rapidly due to less competition.
• C. Fish would develop lungs and begin breathing air immediately.
• D. Many fish would die or become stressed due to insufficient oxygen for respiration.

Answer: (D)

Verified step by step guidance

1. Understand the role of dissolved oxygen in aquatic ecosystems: Dissolved oxygen is essential for fish and other aquatic organisms to perform cellular respiration, which is the process of converting glucose into energy (ATP). Without sufficient oxygen, their ability to generate energy is compromised.
2. Clarify why fish cannot switch to photosynthesis: Photosynthesis is a process performed by plants, algae, and some bacteria to produce energy using sunlight, carbon dioxide, and water. Fish lack the cellular structures (like chloroplasts) required for photosynthesis, so this option is biologically impossible.
3. Explain why fish populations would not increase: Low oxygen levels create a stressful environment, making survival difficult for fish. This would likely lead to a decrease in population rather than an increase, as competition for limited oxygen intensifies.
4. Discuss why fish cannot develop lungs immediately: Evolutionary changes, such as developing lungs, occur over long periods through genetic mutations and natural selection. Fish cannot adapt instantaneously to environmental changes by developing new organs.
5. Conclude with the correct answer: Many fish would die or become stressed due to insufficient oxygen for respiration. Stress and mortality occur because fish rely on dissolved oxygen in the water to sustain their metabolic processes.