Weekly “What is it?”: Elver

The translucent “elver” is a juvenile eel that has drifted thousands of miles to the edges of our coasts. Photo credit: Glenn Conrad

With its ghostly translucence, this small fish is barely visible in the water. In fact, when swimming upright, it resembles a piece of cellophane tape—long, thin, and clear. This lack of coloration is common in young juvenile fish, allowing them to hide in plain sight from ravenous predators. These young ones have traveled a very long, arduous route, and need every bit of protection they can get.

This particular little fish is known as an elver, and is the immature form of the American eel (Anguilla rostrata). To maintain the glasslike quality of their bodies, elvers have small organs and a simple, tubelike digestive system. They do not possess red blood cells until they develop into adults. Interestingly, as juveniles they have sharp fang-like teeth, but seem only to feed on free-floating detritus known as marine snow.

After months in the Atlantic Ocean, juvenile eels drift into the Gulf and make their way into freshwater streams, rivers, and springs to live out their adulthoods. Photo credit: Glenn Conrad

Adult eels spawn in the Sargasso Sea—a large offshore floating “island” of sargassum seaweed in the Atlantic Ocean—that also houses young sea turtles and an entire ecosystem of sargassum-specific organisms. Once born, the eel larvae swim and drift as far as 3000-4000 miles through the Gulf Stream towards the coast. They swim up into freshwater streams and rivers, where they grow into a larger “glass eel” stage, and then into adults. Elvers spend longer times (3-12 months) in this juvenile stage than most fish, likely due to the long swim from the Sargasso Sea. They also grow larger than typical larvae, anywhere from 2 to 12 inches! Their swimming motion is the snakelike undulation common to eels, but they can move forwards and backwards.

Eel larvae are termed “leptocephalus,” which means “slim head” in Latin. This describes the young of over 800 species of eels. Other fish, including tarpon and bonefish, also start out as transparent, laterally compressed larvae. The elver featured in our photos was found off Pensacola Beach in May. As you venture out to the beach this spring, keep your eye out—if you look closely you may just come across a baby eel!


Posted: March 16, 2021

Category: Natural Resources
Tags: Weekly What Is It

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