Most species these days have somewhat tragic stories, as more and more animals head towards extinction. But sometimes the opposite happens, and a species that was thought to be extinct suddenly turns up and everyone is really excited about it. Such is the case with coelacanths, which were thought to have gone extinct around 60 million years ago, and suddenly turned up off the coast of South Africa in 1938.

There are two living species of coelacanth, the West Indian Ocean coelacanth and the Indonesian coelacanth. The first species has been found in waters around Comoros, Kenya, Tanzania, Mozambique, Madagascar and South Africa, while the second lives around Indonesia. Coelacanths dwell in deep waters, from 100 to 500m, and prefer area with lots of underwater caves where they can rest during the day.

A pretty coelacanth. Image by Bruce A.S.Henderson, CC BY 4.0, via Wikimedia Commons

Coelacanths are very strange fish — they are more closely related to reptiles and mammals than they are to most other fish. They have some weird physical traits, including a single, fatty pseudo-lung, a linear heart, and a notochord instead of a vertebral column. They have a hinge at the back of their skulls, which means their mouth can open very wide. They are brown to dark blue in colour, with varying light spots on their scales.

Coelacanths are quite lazy fish – they don’t tend to move very often or very quickly, instead preferring to drift with the currents. They use their fins to stabilize themselves while floating in this manner, and are quite manoeuvrable, as they can do headstands or swim upside-down if they want to. If they need to, they can move more quickly, using their tail fin for short bursts of speed.

But coelacanths don’t like do to this; they are great believers in conserving energy. They live in deep waters so that the cooler temperatures lower their metabolic costs, and rest in caves during the day. When they hunt, they do so lazily, using currents to move along and eating whatever crosses their paths.

Reproduction in coelacanths is also unusual. Unlike most fish, coelacanth eggs develop within the female, and hatch inside mother before she gives birth. While this method of reproduction is common in sharks, it is very rare in bony fish.

While both species of coelacanth are currently threatened, there is a bright side: humans have little reason to catch them, other than for research purposes. Coelacanths have a very oily composition, meaning they taste awful, so they have no value as a food fish. Unfortunately for these guys, they are caught as by-catch, which is not good for their populations. Hopefully we can preserve these unique fish so they don’t go extinct (again).