Why the eel and lung fish considered fishes?

Eels and lungfish are considered fishes because they share the key characteristics that define the class "Pisces":

1. Aquatic Lifestyle: Both eels and lungfish live primarily in water, though lungfish can survive out of water for a limited time.

2. Gills for Respiration: Both eels and lungfish use gills to extract oxygen from the water for respiration.

3. Fins for Movement: Both eels and lungfish have fins, albeit with different shapes and adaptations, which they use for swimming.

4. Scales (usually): Eels and lungfish generally possess scales, although the scales of eels are quite small and embedded in their skin.

5. Vertebrates: Both are vertebrates, meaning they have a backbone and a skeletal system.

6. Reproduction in Water: Both typically reproduce by laying eggs in water.

7. Cold-blooded: Both are cold-blooded, meaning their body temperature is regulated by the external environment.

Eels and lungfish have some unique features:

* Eels: Their elongated, snake-like body shape sets them apart from most other fishes.

* Lungfish: These fishes have adapted to survive in oxygen-poor waters. They possess primitive lungs in addition to their gills, allowing them to breathe air when needed.

While these unique characteristics are important, they do not negate the fact that eels and lungfish share the fundamental features of fishes. Their evolutionary history and shared characteristics place them firmly within the class Pisces.