In one of the following fish, the dorsal fin is modified into suckers

• a. Torpedo
• b. Echeneis
• c. Hippocampus
• d. Neoceratodus

The fish in which the dorsal fin is modified into suckers is Echeneis, commonly known as the remora. These fish have a specialized dorsal fin that forms a suction disk, allowing them to attach to larger marine animals like sharks and turtles.

Key Features of Echeneis

• Suction Disk: The modified dorsal fin acts as a sucker.
• Symbiotic Relationships: Often found riding on larger fish.
• Streamlined Body: Adapted for efficient swimming.

In contrast, the other options do not have this unique adaptation:

Other Fish Options

• Torpedo: Known for its electric capabilities.
• Hippocampus: Commonly known as seahorses, with a different fin structure.
• Neoceratodus: A type of lungfish, not featuring suckers.