Which of the following statements is not true of a fish?

Step 1: Analyze the question We need the statement that is NOT true of fish. Three options are true, one is false.

Step 2: Key concepts

• Poikilothermic (cold-blooded/ectothermic): body temperature changes with the surroundings.
• Homeothermic (warm-blooded/endothermic): body temperature stays constant regardless of the environment, as in mammals and birds.

Step 3: Check each option

• A. Respires with gills: True. Fish take in dissolved oxygen from water through gills.
• B. Covered with scales: True. Most fish have scales (bony fish have cycloid or ctenoid scales, cartilaginous fish have placoid scales).
• C. They are homeothermic: False. Fish cannot regulate their body temperature internally, so it varies with the water temperature.
• D. They are poikilothermic: True. This is the correct description of fish.

Step 4: Answer The statement that is not true of fish is C, they are homeothermic.

Exam tip: Remember that fish, amphibians and reptiles are poikilothermic, while birds and mammals are homeothermic. Think "P for Pisces (fish) and Poikilo". In "NOT true" questions, first find the options that are clearly true and eliminate them. A and D are classic fish facts, and B is also correct, so only C remains.