This week’s episode is about some interesting eels, including the Brantevik eel. A European eel: A leptocephalus, aka an eel larva: A moray eel. It has those jaws you can see and another set of jaws in its throat: Episode transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week, we’re going to learn about the Brantevik eel and some other eels, including an eel mystery. The Brantevik eel is an individual European eel, not a separate species. Its friends knew it as Åle, which I’ve probably misprounounced, so I’m nicknaming it Ollie. So what’s so interesting about Ollie the eel? First, let’s learn a little bit about the European eel in general to give some background. It’s endangered these days due to overfishing, pollution, and other factors, but it used to be incredibly common. It lives throughout Europe, from the Mediterranean to Iceland, and has been a popular food for centuries. The European eel hatches in the ocean into a larval stage that looks sort of like a transparent flat tadpole, shaped roughly like a leaf. Over the next six months to three years, the larvae swim through the ocean currents, closer and closer to Europe, feeding on microscopic jellyfish and plankton. Toward the end of this journey, they grow into their next phase, where they resemble eels instead of tadpoles, but are mostly transparent. They’re called glass eels at this point. The glass eels make their way into rivers and other estuaries and slowly migrate upstream. Once a glass eel is in a good environment it metamorphoses again into an elver, which is basically a small eel. As it grows it gains more pigment until it’s called a yellow eel. Over the next decade or two it grows and matures, until it reaches its adult length—anywhere from two to five feet, or 60 cm to 1.5 meters. When it’s fully mature, its belly turns white and its sides silver, which is why it’s called a silver eel at this stage. Silver eels migrate more than 4,000 miles, or 6500 km, back to the Sargasso Sea to spawn, lay eggs, and die. One interesting thing about the European eel is that during a lot of its life, it has no gender. Its gender is determined only when it grows into a yellow eel, and then it’s mostly determined by environmental factors, not genetics. Until the late 19th century, everyone thought these different stages—larva, glass eel, elver, yellow eel, and silver eel—were all separate animals. No one knew how or even if eels reproduced. The ancient Greeks thought eels were a type of worm that appeared spontaneously from rotting vegetation. Some people thought eels mated with snakes or some types of fish. By the 1950s the eel’s life cycle was more or less understood, but many researchers thought the European eels never made it to the Sargasso Sea to spawn. It was just too far, so they thought the eels that arrived in Europe were all larvae of the American eel, which is almost identical in appearance to the European eel. The Sargasso Sea is off the coast of the Bahamas, so the American eel doesn’t have nearly as far to travel. These days we know from DNA studies that the American and European eels are different species. The European eel is just a world-class swimmer. European eels are nocturnal and may live in fresh water, brackish water, or sometimes they remain in the ocean and live in salt water, generally in harbors and shallows. They eat anything they can catch, from fish to crustaceans, from insect larvae to dead things, and on wet nights they’ll sometimes emerge from the water and slide around on land eating worms and slugs. Many populations don’t eat at all during the winter. Now, back to the Brantevik eel. Brantevik is a tiny fishing village in Sweden. In 1859, an eight-year-old boy named Samuel Nilsson caught an eel and released it into his family’s well to eat insect larvae and other pests. This was a common practice at the time when water wasn’t treated,