Read the following statements and find out the incorrect statement.

Options

A. Dog fish has teeth that are modified placoid scales
B. In fighting fish, ills are covered by operculum while in string ray, gill cover is absent.
C. Air bladder in present in saw fish which regulates buoyancy, while in angel fish, air bladder is absent
D. Mouth of flying fish is terminal while that of great white shark is ventral.

Explanation

To identify the incorrect statement from the provided options, we will analyze each statement step by step based on the information given in the transcript.

### Step-by-Step Solution:

1. **Understanding the First Statement:**
- The statement mentions that dog fish has stethes, which are modified placoid scales.
- The dog fish, scientifically known as Scholeodon, is a cartilaginous fish (class Chondrichthyes).
- The statement is correct because the teeth of cartilaginous fish are indeed modified scales.

2. **Analyzing the Second Statement:**
- This statement discusses the gills of the fighting fish and stingray.
- The fighting fish (Betta) is a bony fish (class Osteichthyes) and has an operculum covering its gills.
- The stingray (Trigon) is a cartilaginous fish and lacks an operculum.
- This statement is also correct.

3. **Evaluating the Third Statement:**
- The statement claims that the air bladder is present in the sawfish and absent in the angelfish.
- The sawfish (Pristis) is a cartilaginous fish and does not have an air bladder.
- The angelfish (Pterophyllum) is a bony fish and does have an air bladder.
- This statement is incorrect because it reverses the presence of the air bladder in these fish.

4. **Reviewing the Fourth Statement:**
- This statement compares the mouth positions of the flying fish and the great white shark.
- The flying fish (a bony fish) has a terminal mouth, while the great white shark (a cartilaginous fish) has a ventral mouth.
- This statement is correct as it accurately describes the mouth positions of both fish.

### Conclusion:
The incorrect statement is the third one, which incorrectly states the presence of the air bladder in the sawfish and angelfish.

### Final Answer:
The incorrect statement is: **"The air bladder is present in the sawfish, which regulates buoyancy. While in angelfish, air bladder is absent."**

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