The hippocampus is a fish. Although there are great differences between seahorses and fish in appearance, they are out-and-out fish. Seahorses have many characteristics of fish, such as breathing through gills, which is quite different from aquatic mammals. Secondly, it has fins. Although the shape of fins is quite different, the structure is still the same. In addition, it can only live in water. Although it is not good at swimming, it has high predation efficiency.

1. Breathing through gills: The hippocampus is a fish because it has the characteristic of breathing through gills. Unlike the lungs of terrestrial animals, gills mainly get oxygen from water. When water flows through gill filaments, gas will be exchanged. Of course, it's not just fish that breathe through gills. Amphibian larvae also have gills, as do some aquatic crustaceans, so it depends on other characteristics.

2. Having fins: As we all know, fish have fins. Although seahorses look different from fish in appearance, they also have fins. It has no pelvic fin and caudal fin, dorsal fin is between trunk and tail, anal fin is short, but pectoral fin is developed. Unlike most fish that use caudal fins, hippocampus mainly relies on dorsal fins for swimming.

3. Life in water: Hippocampus lives in water, usually likes to stay in the slow flow of coral reefs, and is not good at swimming. It usually fixes itself with coral and other objects to avoid being washed away by rapids. Due to physical structure and other reasons, this animal is slow to move, but its predation efficiency is still very high.