top of page

134. Yellowmargin Moray Eel (Gymnothorax flavimarginatus) (breathing mechanism)


All animal life needs oxygen to survive. Fish breathe through gills, which allow for the exchange of oxygen and carbon dioxide under water. The water containing necessary oxygen is pumped over the gills. These gills are composed of comb-like filaments called gill lamellae, which help increase the surface area for an effective gas exchange. These filaments contain capillaries where the blood picks up the oxygen that's dissolved in the water. This mechanism is possible thanks to the constant movement of the fish’s opercula, the bony covers that protect their gills.

However, moray eels such as the Yellowmargin Moray Eel (Gymnothorax flavimarginatus) figuring in this underwater videoclip, lack these opercula, and their small, circular gills are located on the flanks far posterior to the mouth. To create the indispensable water flow over their internal gill chamber that provides them with the necessary oxygen to live, they need to orally pump the water by constantly opening and closing their mouths. Unfortunately, way too often scuba divers see this life-sustaining mouth movement as threatening, although it is unjustified.

Gills are also a well sought after habitat for many species of marine parasites. Copepods and leeches are amongst these ectoparasites (ectoparasites are parasites that do not life inside their host but that prefer to attach themselves or move on the outside of their hosts) which are often found on gills.


To film underwater, you must get close to your subject, really close. If your picture or underwater video footage is not good enough, it's often because you were too far away from your subject. Way too often, scuba divers take underwater pictures or film moray eels from too far away, preferring to stay at what they consider a safe distance and using their zoom to get a better shot of the impressive and threatening-looking animal.

However, zooming in underwater is not recommended because water absorbs a lot of colour and light, and in a big space full of water, there are often many suspended particles, even on a day with good visibility. Filming through this big mass of water will drastically decrease the quality of your image or underwater footage.

Some underwater videographers will try to compensate for the absorption of light in water by adding more light with their video lights (increasing the strength) or by increasing the ISO setting of their camera or opening their diaphragm. However, adding more or increasing the strength of the light beam of the video lights to a big water mass will result in more backscatter, which are little dots and specks created by light reflecting on small suspended particles in the water column. And if you increase the ISO setting in your camera, you will create more “noise” in your footage.

The only way to avoid getting poor images underwater is by moving close to your subject. Moray eels, with their opening and closing mouth full of long and threatening teeth, can sometimes be intimidating, but unless you’re an octopus, you have nothing to fear.

Join us on a journey of discovery and entertainment as we explore fascinating marine wildlife topics and explore the many exciting underwater adventures on our YouTube channel and our Facebook page!

Take the plunge and learn to create stunning underwater videos with our online Marine Wildlife Videography course!


bottom of page