"Thermal stress" can occur when temp changes more than 2-3 F in 24 hours.

• A. Hypothermia
• B. Thermal stress
• C. Solubility
• D. Toxicity

Answer: (B)

Rapid temperature changes place stress on aquatic animals because they are ectotherms; their body temperature follows the surrounding water, so a fast change forces their physiological systems to adjust quickly. When water temp shifts by more than about 2–3 °F within 24 hours, the animals experience thermal stress. This stress can raise metabolic rate, increase oxygen demand, disrupt enzyme function, and weaken immune defenses, leading to slower growth or higher disease risk, even if the average temperature remains suitable. The term thermal stress specifically describes stress from temperature changes, not hypothermia (an abnormally low body temperature), not solubility (how substances dissolve), and not toxicity (harm from chemicals).