That's A Moray Monday: The Less Salty Edition

So there you are, relaxing in a refreshing freshwater stream after trekking through the verdant bush in some tropical coastal rainforest in Borneo. You're relaxed because you realize that you're "safe as houses" from the typical coastal marine nibblers, stingers, and biters--soaking, as you are, in freshwater a good kilometer from the ocean. You rest your tired back against a big rock in the clear, flowing stream and close your eyes for a quick nap--which is about when you feel the almost meter-long eel begin to snake its way up your pant leg.

Welcome to the territory of the Freshwater moray.

Freshwater moray
Gymnothorax polyuranodon

It may come as a surprise that some species of moray spend a majority of their time in freshwater. None of the alleged "freshwater" morays, however, are exclusively so. While G. polyuranodon can live in lotic or lentic (flowing or standing) freshwater, it can also be found in brackish and estuarine conditions as well.

The Freshwater moray is a facultatively catadromous species, meaning it reproduces in the sea but spends most of its life in fresh water. In this regard, the Freshwater moray is similar to its cousin the European eel (Anguilla anguilla) which is generally believed to spawn in the Sargasso Sea and then eventually migrate back to European streams and lakes. I won't get into the remarkable cellular and physiological dynamics involved in osmoregulation across such different aquatic habitats. Suffice to say your swollen ankles after eating a big plate of salty kahlua pork 'aint nothing compared to gill energetics moving from a freshwater stream to a hypersaline tropical lagoon.

Freshwater morays are found throughout the Indo-Pacific in Sri Lanka, Indonesia, Borneo, Papua New Guinea, the Philippines, and Fiji. They have also been reported in Micronesia in Palau, and as far south as Australia and New Caledonia. The species has been reported to attain a length of approximately 92.5 cm. The body is yellow in color with rust-brown to black spots, a bit like a leopard, along the length of the eel. The spectacular markings combined with its ability to live in freshwater makes the Freshwater moray particularly attractive to the home aquarium trade. As a result, the species is considered highly vulnerable to exploitation and local depletion throughout its range.