Which one of the following is a true fish ?

Options

A. Cray fish
B. Cuttle fish
C. Flying fish
D. Jelly fish

Answer

To determine which of the given options is a true fish, we need to analyze each option based on their classification and characteristics. Here's a step-by-step solution:

### Step 1: Understand the Definition of True Fish
True fish are aquatic animals that possess specific structures such as gills, scales, and a streamlined body. They belong to the subphylum Vertebrata, specifically within the class Actinopterygii (ray-finned fishes) or class Chondrichthyes (cartilaginous fishes).

### Step 2: Analyze Each Option
1. **Grey Fish**: This option refers to a type of fish that is not classified under the true fish category. It belongs to the phylum Arthropoda, which includes invertebrates like crabs and insects. Therefore, it cannot be a true fish.

2. **Cuttlefish**: Cuttlefish are mollusks, belonging to the class Cephalopoda within the phylum Mollusca. They do not possess the characteristics of true fish, as they are not part of the fish classification.

3. **Flying Fish (Exocetus)**: The flying fish belongs to the class Actinopterygii, which is part of the true fish category. They have a streamlined body, scales, and gills, making them a true fish.

4. **Jellyfish**: Jellyfish are not fish at all; they belong to the phylum Cnidaria and are classified as invertebrates. They do not have the structures that define true fish.

### Step 3: Identify the Correct Answer
Based on the analysis, the only option that fits the definition of a true fish is the **Flying Fish (Exocetus)**.

### Conclusion
The correct answer is **Flying Fish (Exocetus)**, as it is classified under true fish with the necessary characteristics.

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