How does the Alaska blackfish (Dallia pectoralis) survive in waters with temperatures as low as 5°F?

• A. It migrates to deeper, warmer waters during winter.
• B. It can breathe atmospheric oxygen using a modified esophagus.
• C. It enters a state of hibernation and stops all metabolic activity.
• D. It produces antifreeze proteins to prevent its blood from freezing.

Answer: (B)

Verified step by step guidance

1. Understand the environmental challenge: The Alaska blackfish lives in extremely cold waters, where temperatures can drop as low as 5°F. This poses a risk of freezing and oxygen depletion in the water.
2. Identify the adaptations listed in the problem: The options provided include migration to warmer waters, breathing atmospheric oxygen using a modified esophagus, hibernation with halted metabolic activity, and production of antifreeze proteins.
3. Evaluate the biological feasibility of each adaptation: For example, migration to deeper waters may not be possible if the fish remains in shallow habitats, and hibernation with halted metabolism is rare in fish. Consider the unique physiological traits of the Alaska blackfish.
4. Focus on the correct adaptation: The Alaska blackfish has a modified esophagus that allows it to breathe atmospheric oxygen. This adaptation is crucial for survival in oxygen-depleted environments during winter.
5. Conclude the reasoning: The ability to breathe atmospheric oxygen using a modified esophagus is a specialized adaptation that enables the Alaska blackfish to survive in extreme cold conditions without relying solely on dissolved oxygen in the water.