Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Anguilliformes
Family: Muraenidae

Basics

  • Morays are a family of eel found worldwide.
  • Most of the over 200 species are marine, but some live in brackish or freshwater 
  • The name moray is derived originally from the Greek word, muraina, which is a kind of eel that is common in the Mediterranean
  • They’re completely scaleless.
  • They have poor vision and mostly rely on chemoreception (a physiological process whereby organisms respond to chemical stimuli) to catch prey. They even have very visible nostrils. Their vision is not that important as they’re mostly nocturnal.

Evolution

Biology

  • At first glance, they look like snakes, because of their lack of apparent fins, but they’re really just fish that have evolved to live in small and narrow crevices.
  • Contrary to belief, they do have fins. Their dorsal fin goes all the way to the back and joins with the caudal and anal fins giving them a Mohawk style fin.
  • They lack pectoral and pelvic fins, so as a result, their sides and bottom are fairly smooth.
  • Their bodies and the insides of their mouth are usually patterned.
  • Most species have big sharp teeth to grab slimy, slippery fish. But some species specialize in crustaceans and other hard shelled animals, so their teeth are blunt to crack shells open.
  • Morays are covered in mucus and in some species, this mucus is toxic.
  • They have a bunch of cells on their skin called goblet cells. These cells are in charge of producing the mucus. Morays have them in higher densities than other eels, and are extra slimy.
  • Different types of moray produce mucus in different proportions and areas of their body depending on their lifestyles. In general terms, the mucus protects them from abrasions caused by sand or sharp edges in hard formations (rocks, corals, etc.)
  • Reef-associated morays such as the geometric moray have a pretty much uniform level of mucus all over their bodies, as they need slide through small crevices.
  • Garden eels (not morays, but a helpful comparison) spend most of the time in sand, so their dorsal side has comparatively more mucus than the rest of their body.
  • Ribbon eels (currently considered a type of moray, but taxonomy still being studied) make burrows in the sand. The copious amount of mucus they produce acts as glue, holding the sand in their burrows together and preventing it from collapsing.
  • One of the coolest things about morays is their jaws. They have their regular (oral) jaws with big teeth but h they have a second jaw called the pharyngeal jaw.
  • This second jaw sits in the morays throat. Once the oral jaw grabs prey, the pharyngeal jaw bites it and pulls it into the animal’s gullet.
  • They’re the only animal known to do this. Most other fish use suction to pull their prey in.
  • You often see them opening and closing their mouths. This is just their way of forcing water through their gills.
  • If you move in the water you generate waves. Aquatic animals have the issue of generating strong waves when they lunge at prey, which could potentially move the prey away from them.
  • Morays have a large mouth with opening on the sides, so as they lunge they let water go through their mouths to prevent wave generation.
  • Some animals, like the giraffe, become longer than their relatives by stretching their vertebrae. They famously have the same number of neck bones as we do. But morays have become elongated by evolving more vertebrae. The number varies by species, but the cool thing is that for every new precaudal vertebra they add, they also add a tail vertebrae.

Moray Reproduction:

Behaviour

  • Morays are opportunistic ambush predators and are known to catch anything from fish to cephalopods and crustaceans.
  • Morays have few predators and the larger species are often the apex predator in their ecosystems. 
  • Giant Moray eels have been observed cooperating with groupers on hunts.
    • Groupers are open water hunters. Their prey hides from them in corals.
    • Giant morays live in the corals and corner their prey in small holes to eat them. Their prey is forced to go into open water to escape from them.
    • To initiate cooperation, the grouper will go to a morays resting place and shake their head vigorously. The moray then comes out and swims together with the grouper.
    • Then the moray can try to catch fish in the reef, if it tries to escape the grouper gets it. If it gets scared by the grouper, then the moray can catch it.
    • There’s video of this here in “supporting information” https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0040431
  • Most morays live in warm waters in tropical or subtropical environments, but there are a few species that live in more temperate waters (like the California Moray)
  • Sometimes they can tie themselves into knots to create leverage as they pull prey out of a crevice. 

Did you know that…

  • Morays are sometimes kept as pets
    • The Romans were rumoured to have pet morays in special ponds, and apparently fed them slaves.
  • In modern days, species such as the snowflake, zebra, and golden-tailed morays are kept in aquariums. Other species have also been seen but are quite expensive.
  • Morays are not recommended because they carry ciguatera. This can give people neurological, gastrointestinal, and cardiovascular problems.
  • According to the CDC:  People who have ciguatera may experience nausea, vomiting, and neurologic symptoms such as tingling fingers or toes. They also may find that cold things feel hot and hot things feel cold. Ciguatera has no cure. Symptoms usually go away in days or weeks but can last for years. People who have ciguatera can be treated for their symptoms.
  • Shrimp are often seen “cleaning” morays. This is a symbiotic behaviour where the shrimp gets an easy meal, and the moray gets its external parasites removed.

Species We Think Are Cool

Freshwater Moray Eel

  • This species is found in freshwater in the Indo-Pacific region
  • Its about 1 m long.
  • Its saliva is slightly toxic and bites can result in infections.

Mediterranean Moray

  • Has toxic blood
  • Was believed to be kept as pets by the Romans

Snowflake Moray

  • It has blunt teeth to crush hard-shelled animals.

Ribbon eel

  • It has extended protruding nostrils.
  • It’s believed to be protrandric hermaphrodite, meaning they’re born male and later in life become female.
  • Juveniles are black but mature individuals are colourful. Males are blue and yellow and females are all yellow.
  • Females can be up to 130 cm long.

Snyders moray

  • The smallest moray