Are Seahorses Considered Fish?

By Nick A. Romero, Biologist and environmental educator. November 1, 2022
Are Seahorses Considered Fish?

We group animals together taxonomically for many reasons. The research which is undertaken to investigate the animal kingdom is vast and incredibly complicated, so classifying animal species helps us to better understand them. Another reason is that the common names we give animals can be very confusing. A koala bear is not actually a type of bear, just as a guinea pig isn't a type of pig. One similarly misleading marine animal is the seahorse (Hippocampus hippocampus). While their head is shaped similarly to the equine mammal, it is difficult to imagine them in stirrups.

For this reason, AnimalWised wants to get to the bottom of the seahorse. Specially, we want to know are seahorses considered a fish? We answer this by looking at the classification of seahorses.

You may also be interested in: Fun Facts About Seahorses

Is the seahorse a fish or a mammal?

Due to their appearance and moniker, it is understandable why we may not know what type of animal is a seahorse? While their head does look a little like that of the land mammal known as the horse, the similarities pretty much end there. Seahorse have no fur, hooves, manes or many other of the core characteristics which make up the horse. Although there are types of marine mammals, none of them are a type of horse.

For this reason, we may wonder what other types of aquatic animals the seahorse resembles. When we think of fish, we often think of a long animal with fins at the sides, top and tail. For this reason, the seahorse does not appear to be a typical fish. However, this is exactly what they are. Although unique and very distinctive, the seahorse is considered a fish.

Although we may think of fish swimming in a horizontal position, seahorses do so upright. They have an ‘S’-shaped body which is uncommon among animals, both aquatic and terrestrial. Although they may not look like a typical fish, they are. In some ways, they can be considered the exception which proves the rule.

There are many factors which help us to classify animals. Take a look at our types of freshwater fish list to learn about just one of them.

Why is the seahorse considered a fish?

We now know a seahorse is considered a fish, despite their peculiarities in terms of body shape. The reason for this is because of certain characteristics which all fish species possess:

  • Musculoskeletal system: all fish have vertebral column, jaw, ribs, cranium and intramuscular bones. The seahorse is no exception. Most fish are either cartilaginous or bony fish, although there are other classifications.

  • Fins: they have a small dorsal fin which is used to propel them through the water.

  • Respiration through gills: they absorb dissolved oxygen from the water and expel carbon dioxide into it. Discover more animals that breathe through gills in our related article.

  • Presence of a swim bladder: a bladder which is filled with gas and helps the buoyancy of the animal.

Although they have the basic characteristics which mean they are a type of fish, seahorses also have their own specific characteristics. We explain these in more detail below.

Are Seahorses Considered Fish? - Why is the seahorse considered a fish?

What kind of fish is the seahorse?

Fish are the most diverse type of vertebrate animals. In fact, according to at least one fish information database, there are more species of fish than there are of all the other vertebrates combined. In this context, we can see why it is important to consider the more specific traits of the seahorse so we can contextualize them with other fish species:

  • Actinopterygii class: the first classification of seahorses is into this group of bony fish with ray-type fins. These fins are formed from webs of skin, supported by bony spines.

  • Syngnathiformes order: this order brings together fish with elongated bodies, somewhat narrow and surrounded by bony rings. The mouth is tubular in shape and small. Perhaps the most peculiar feature of this group is that males are dedicated to the breeding and care of the embryos, which they keep in an osmoregulated bag until they develop.

  • Syngnathidae family: these are fish that live in temperate or tropical seas worldwide. Some are located in shallow waters, but others in the open sea. In addition to an elongated snout, the jaws are characterized by being fused together. There is an absence of pelvic fins and the body is covered by bony armor plates. This armor gives them a rigid body so they are relatively slow to swim compared to other types of fish, although they can control their movements very precisely.

  • Hippocampus genus: this is the last classificaiton of seahorses into their specific species. In relation to the number of species, these are very diverse, and vary according to the source [1] [2]. For this reason, the total amount of seahorse species ranges from 41 to about 72. Most sources suggest there are at least 47 species, something the National Oceanic and Atmospheric Administration (NOAA) supports[3].

  • Movement: being a type of fish that does not have the same ability to swim as other species, seahorses usually cling to corals, plants or any other surface with their prehensile tail. Their habitat is made up of seagrass beds, coral reefs, mangroves or estuaries, all ecosystems that provide them with protection and the possibility of anchoring.

  • Swimming position: another of the traits that characterizes the seahorse corresponds to the fact they are one of the few fish that swim upright and move vertically.

  • Reproduction: in relation to their reproductive behavior prior to the fertilization of the eggs, seahorses have a complex and long period of courtship. Various species of these fish also form lasting bonds, while others frequently change partners.

  • Diet: seahorses are considered a carnivorous fish. They mainly feed on small crustaceans, other invertebrates and larvae.

  • Conservation: the seahorse is a type of fish that causes concern in the scientific community. Although we do not know how many types of seahorse species there are in the world, it is known they are very susceptible to environmental change. In some cases, it has been possible to establish the conservation status of some species, which have been included in the categories of vulnerable and endangered.

Learn more about fish species as a whole with our related article on whether all fish have scales?

If you want to read similar articles to Are Seahorses Considered Fish?, we recommend you visit our Facts about the animal kingdom category.


1. Lourie, Sara A., Pollom, Riley, A., & Foster, S. J. (2016). A global revision of the Seahorses Hippocampus Rafinesque 1810 (Actinopterygii: Syngnathiformes): Taxonomy and biogeography with recommendations for further research. Zootaxa, 4146(1), 1–66.

2. STI. (2020). Hippocampus. Retrieved from:

3. NOAA. (2021). How do seahorses differ from all other animals? Retrieved from:

  • Animal Diversity Web. (2020). Available at:
  • IUCN. (2022). The IUCN Red List of Threatened Species . Version 2022-1. Available at:

Write a comment

Add an image
Click to attach a photo related to your comment
What did you think of this article?
Are Seahorses Considered Fish?
1 of 2
Are Seahorses Considered Fish?

Back to top