Leptocephalus, The Transparent Eel Larva

Credit: Mie Prefecture Fisheries Research Institute

Transparent Fish (Leptocephalus). Credit: Mie Prefecture Fisheries Research Institute

The marine eels and other members of the Superorder Elopomorpha have a leptocephalus larval stage, which are flat and transparent. This group is quite diverse, containing 801 species in 24 orders, 24 families, and 156 genera. They arose in the Cretaceous period 140 million years ago.

Fish with a leptocephalus larva stage include eels like the conger, moray eel, and garden eel. The conger eel is the one whose larva was captured by the Mie Prefecture Fisheries Research Institute in Japan.

Credit: Mie Prefecture Fisheries Research Institute

Credit: Mie Prefecture Fisheries Research Institute

Leptocephali have laterally compressed bodies that contain jelly-like substances on the inside, with a thin layer of muscle with visible myomeres on the outside. They have a simple tube as a gut. They have dorsal and anal fins, but they lack pelvic fins. They also don’t have any red blood cells, which they only begin producing when they change into the juvenile glass eel stage. They also possess fang-like teeth that are present until metamorphosis, when they are lost.

Leptocephali differ from fish larvae because of their size and their long larval periods, which last between three months to more than a year. Their anguilliform swimming motions allow them to move forwards and backward. They appear to feed on marine snow, tiny free-floating particles in the ocean.

8 Comments on "Leptocephalus, The Transparent Eel Larva"

  1. Madanagopal.V.C | January 12, 2013 at 10:01 pm | Reply

    The transparent Eel larva reminds me of the transparent jelly fish which also belongs to the cretaceous period 140 million years ago. Probably there were not much predators for these fishes in the early period, they themselves feeding on free floating particles. Even human beings at the embryological stage are transparent only. They add pigments and hair later on to face the environment in their later life. Red blood corpuscles are required to transport oxygen from lungs whereas the fish can breath through their gills by drinking dissolved oxygen in water.

  2. can it develope inside you possibly

    • Not at all. No more than kittens or oranges can develop inside you.

      They have to breathe, live in seawater, and can only eat bits of plankton and other marine debris. Unless you also have a large ocean and sunlight inside you, you can not host these. If you swallowed one, you would digest it (and people do eat eel!)

      They do superficially look vaguely like certain parasitic worms, so I can see the reason for your question, but they are not biologically parasites.

  3. But is there actually risk of mistakingly consuming one? Are they actually present and have been found in drinking water?

    • Even if you did accidentally swallow one….it wouldn’t hurt you in any way. And NO…they have not been found in drinking water. That’s just another “Fake News” article. The Transparent Eel are found in the Ocean.

  4. I found one of these on the beach. Are they very hard to take care of? I was thinking of taking it back with me.

  5. there was one of those things in my water cup

  6. So today I received my “new” washing machine that I ordered online. I opened it and to my surprise it was already used and returned once. I was moving it around and realized that there is still water inside from the previous customer. The manual and some of the items that came with it were all covered with some kind of mold. I later tried to clean it and see if I can use it. When I poured down some bleach into the designated area with a small hole (1/3 of an inch), something popped out of it. At first I thought it as just a bubble from the bleach, but I looked again and it looked like it had eyes. My mum confirmed it too and when I googled it and I saw this picture and am currently in shock. Is I possible that this thing was in my washing machine??

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