Which of the following statements is incorrect regarding circulatory system of fishes?

Options

A. Fishes have two chambered heart with an atrium and a ventricle
B. Only deoxygenated blood is pumped through their heart
C. Mixing of oxygenated and deoxygenated blood occurs in ventricle
D. Oxygenation of blood occurs at gills

Answer

To determine which statement is incorrect regarding the circulatory system of fishes, let's analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement:** Fishes have a two-chambered heart consisting of an atrium and a ventricle.

**Analysis:** This statement is correct. Fishes possess a two-chambered heart, which includes one atrium and one ventricle. This structure is characteristic of the fish circulatory system.

**Hint:** Remember that the heart of fishes is adapted for their aquatic environment, having only two chambers.

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### Step 2: Analyze the Second Statement
**Statement:** Only deoxygenated blood is pumped through the heart.

**Analysis:** This statement is incorrect. While it is true that the heart of fishes primarily pumps deoxygenated blood to the gills for oxygenation, it also pumps oxygenated blood to the rest of the body. Therefore, this statement does not accurately describe the function of the fish heart.

**Hint:** Consider the flow of blood in fishes: it goes from the heart to the gills and then to the body.

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### Step 3: Analyze the Third Statement
**Statement:** Mixing of oxygenated and deoxygenated blood occurs in the ventricles.

**Analysis:** This statement is correct. In fishes, the ventricle receives deoxygenated blood from the atrium and pumps it to the gills, where it gets oxygenated. However, there is no mixing of oxygenated and deoxygenated blood in the ventricle as in amphibians.

**Hint:** Think about how fishes have a single circulatory system and how blood flows through their heart.

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### Step 4: Analyze the Fourth Statement
**Statement:** Oxygenation of blood occurs at the gills.

**Analysis:** This statement is correct. In fishes, oxygenation of blood indeed occurs at the gills, where oxygen from the water diffuses into the blood.

**Hint:** Remember that gills are specialized structures for gas exchange in aquatic organisms.

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### Conclusion
After analyzing all the statements, the incorrect statement regarding the circulatory system of fishes is the second one: "Only deoxygenated blood is pumped through the heart."

**Final Answer:** The incorrect statement is the second one.

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