---
title: "Eel Bones: Are Eels Bony to Eat, and What Their Bones Reveal"
url: https://thesea.org/eel-bones/
date: 2024-03-06
modified: 2026-11-13
lang: en
author: "Blane Perun"
description: "Eels are bony fish with 100+ vertebrae. How eel bones affect eating, why the skeleton wastes away before spawning, and what otoliths and archaeological bones reveal."
categories:
  - "Eel Q&A"
image: https://thesea.org/wp-content/uploads/eel-skeleton-thesea-org-blane-perun-1024x572.webp
word_count: 3879
---

# Eel Bones: Are Eels Bony to Eat, and What Their Bones Reveal

[TheSea.Org](/)▸[Eels](/eels/)▸Eel Bones

# Eel Bones — Bony to Eat, Useful to Science

Eel Q&A
By [Blane Perun](/about-blane-perun/)
November 8, 2026
17 min read

The short answer
Yes, eels have bones. They are bony fish with a skull, jaws and a very long backbone: about 114 to 115 vertebrae on average in the European eel and around 750 in the slender snipe eel. Freshwater eels fillet off the spine almost bone-free, conger is bonier towards the tail, and eel ear stones (otoliths) record an eel’s age and whether it lived in fresh or salt water. Why eel must always be cooked, and whether moray is safe, is covered in [can you eat eel](/can-you-eat-eel/).

Eel bone facts

SkeletonBone, not cartilage
SpineEuropean eel 104–120 (mean ~114.6); American ~107
Record count~750 vertebrae (slender snipe eel)
Pin bonesFew in freshwater eels; conger bonier towards tail
Pelvic bonesNone (no pelvic fins)
Ear stonesOtoliths record age and salinity history
Culinary useFried eel-spine snacks in Japan (hone senbei)

Do eels have bones?
Yes. Eels are bony fish, not cartilaginous ones. Every true eel has a bony skull and jaws, gill arches, a very long backbone and fine bony rays supporting its fins. The European eel averages about 114 to 115 vertebrae, and one deep-sea eel has around 750, more than any other animal.

The idea that eels are boneless comes from three things. Their snake-like body hides the skeleton completely; their skin is smooth and slimy, with the scales of freshwater eels tiny and buried in the skin and those of morays and congers lost altogether; and most people meet eel as a soft, glazed fillet on rice or a slice of smoked fish, with the backbone already taken out. Underneath, an eel is built on the same plan as a trout or a cod. It belongs to the ray-finned fishes, the group that contains almost all familiar fish, and within that group to the Elopomorpha, an old lineage that also includes tarpon and bonefish and whose members all start life as a flat, transparent larva called a leptocephalus. That larva is so watery and see-through that its skeleton is barely mineralised; the hard, fully ossified skeleton develops as the larva turns into a glass eel and then grows into an adult.

This page is about the bones as people actually meet them: how many there are, which ones are missing, what happens to them when you cook or eat an eel, why an eel’s skeleton wastes away before it spawns, and how ear stones and archaeological bones have become scientific records. For a bone-by-bone tour of the anatomy itself, see our [eel skeleton](/eel-skeleton/) guide; for the strange double jaws of morays, see the [moray eel skull](/moray-eel-skull/).

![eel bones: Eel Bones: Are Eels Bony to Eat, and What Their Bones Reveal](https://thesea.org/wp-content/uploads/eel-bones-thesea-org-by-blane-perun.webp)eel bones
How many vertebrae does an eel have?
Far more than most fish. Freshwater eels have roughly 103 to 120 vertebrae depending on the species and the individual, morays and congers have similarly long spines, and the slender snipe eel of the deep Atlantic has around 750.

The best data come from the two Atlantic freshwater eels, because their vertebrae have been counted by the thousand. In a 1980 review of old and new counts, the Danish biologist Jan Boëtius gave a range of 104 to 120 vertebrae for the European eel, *Anguilla anguilla*, with a mean of about 114.6, and 103 to 112 for the American eel, *Anguilla rostrata*, with a mean of about 107.2. The Dutch Naturalis fish key gives the usual European range as 110 to 119, and the classic *Fishes of the Gulf of Maine* by Bigelow and Schroeder summed it up as about 107 in the American eel against about 114 or 115 in the European. Each of those vertebrae is small, so an eel’s backbone is a long chain of many short links rather than a few large bones.

Eels did not get long by stretching each bone. In morays, studies of the skeleton show that the elongated body comes from an increase in the number of vertebrae rather than from longer individual vertebrae or a much thinner body, and the extra vertebrae were added unevenly to the trunk and tail regions over the course of evolution, in a different pattern from snake eels and congers. The extreme case is the slender snipe eel, *Nemichthys scolopaceus*, a thread-like deep-water eel up to about 1.5 m long that weighs only a few ounces; it is credited with around 750 vertebrae, the highest count recorded for any animal.

One practical consequence is that the bones of an eel do not behave like those of a short-bodied fish on the plate or in the ground. A single eel leaves behind hundreds of small, similar-looking vertebrae, which matters both to a diner picking through a stew and, as we will see, to an archaeologist counting bones from a medieval rubbish pit.

How did counting eel bones help solve the eel mystery?
It gave scientists a reliable way to tell the European and American eels apart, even as larvae drifting in the same patch of ocean. Johannes Schmidt, the Danish biologist who traced both species to the Sargasso Sea in the early 1900s, identified the total number of vertebrae as the best distinguishing character between them.

The two Atlantic eels look almost identical, and both spawn in the Sargasso Sea before their larvae drift to opposite sides of the Atlantic. A larva caught in mid-ocean could belong to either. Schmidt found that the vertebral count was set early in development and differed consistently between the two, so a count of the backbone, or of the muscle blocks in a larva, could sort them. Later workers found that in larvae longer than about 40 mm the number of muscle blocks (myomeres) exceeds the final vertebral count by about one, which let larval counts be compared with adult skeletons. Schmidt’s method was precise enough that later researchers followed his rules exactly: the short first vertebra, the atlas, is counted as number one, and the last hourglass-shaped vertebra is taken as the next-to-last.

The overlap between the species is small. In Boëtius’s compiled data the two ranges met mainly at 111 vertebrae, a count shared by about 1.1 percent of European and 0.6 percent of American specimens. That separation made the vertebral count a key piece of evidence in one of the twentieth century’s more colourful ichthyological arguments. In 1959 the zoologist Tucker proposed that European eels never made it back to the Sargasso Sea, that Europe’s eels were really American eels, and that the difference in vertebrae was caused simply by water temperature during early development. The hypothesis was never verified and was rejected in later studies, including Bruun in 1963 and Sinha and Jones in 1975. Boëtius’s own survey turned up a few European-caught eels with only 105 to 110 vertebrae in northern Europe, which he attributed partly to stray American eels, a reminder that the backbone carries a signal of where an eel was born.

Genetics has since taken over the job; DNA markers now identify the two species and their hybrids. But for nearly a century the most reliable test of an Atlantic eel’s identity was to count its bones.

Which bones does an eel not have?
Eels have lost their pelvic fins and the bones that support them, and many species have lost their pectoral fins too. Their dorsal, tail and anal fins have merged into one long fringe supported by many fine bony rays.

All true eels lack pelvic fins, the paired fins that in most fish sit on the belly. Freshwater eels keep small, well-developed pectoral fins behind the head, and for years anatomists thought they had lost the scapula, one of the bones of the shoulder girdle. More careful staining showed that freshwater eels do have both a scapula and a coracoid; the scapula gives muscles an anchor that helps the head move and strengthens the body’s swimming waves. Morays have gone further and lost the pectoral fins altogether, which suits an animal that spends its life pushing through holes in a reef. Our [moray eel skeleton](/moray-eel-skeleton/) page explains how that finless frame works.

The fins that remain are fused. In an eel the dorsal fin, tail fin and anal fin run together into a single ribbon around the rear of the body. Each part of that ribbon is held up by slender bony rays, so although an eel looks finless at first glance it has a great many tiny bones in its fins. Freshwater eels also have paired frontal bones on top of the skull, a feature linked to a stronger cranium that helps them burrow into mud and push under stones and logs. Eels are, in short, not simplified fish. Their skeletons have been reshaped for a life of wriggling, burrowing and long-distance swimming, with some parts removed and others multiplied.

| Eel | Vertebrae (approx.) | Pectoral fins | Pelvic fins |
| --- | ------------------- | ------------- | ----------- |
| European eel (*Anguilla anguilla*) | 104–120, mean ~114.6 | Yes | No |
| American eel (*Anguilla rostrata*) | 103–112, mean ~107 | Yes | No |
| Moray eels (Muraenidae) | Many; length comes from extra vertebrae | Absent in most species | No |
| Slender snipe eel (*Nemichthys scolopaceus*) | ~750 | Yes | No |

Are eels bony to eat?
Freshwater eels are easy: the cook lifts out the backbone and the flesh comes away in a long, almost boneless piece, with only tiny bones that soften in cooking. Conger eels are bonier, especially towards the tail.

The classic example is Japanese *kabayaki*, the grilled, sauce-glazed eel served as unagi. The eel is split, gutted and boned before it is skewered and grilled. Regional style even decides which way it is opened: in the Kanto region around Tokyo the eel is slit down the back, butterflied, cut into shorter fillets, steamed and then grilled again, while in the Kansai region around Osaka it is slit down the belly and grilled directly without steaming. Either way the spine is removed, and what reaches the table is effectively boneless. Japanese cooks note that the few tiny bones left behind become tender in cooking.

Congers are another matter. In Mallorca, where conger (*congrio*) is a popular market fish, buyers are told that the smaller the slice, the more bones it has. The open slices cut from the belly near the head are practically bone-free and cost more; the closed, rounder slices from further down the body are much bonier. That is why conger tail sections tend to go into stews and soups, where long cooking makes the bones easier to deal with, while the thick front portions are fried, grilled or roasted.

Part of the reason some fish are bonier than others lies in the small spicule-like bones that sit in the muscle, called intermuscular bones. They ossify from tendons and occur only in the more basal lineages of bony fish, which is why carp and their relatives, all of which have them, are known for fine bones in the fillet. Eels belong to one of those early-branching lineages, which helps explain why cooks fillet them carefully. For freshwater eels the practical problem is small, but anyone feeding eel to young children should check the flesh, as with any fish that has fine bones.

Can you eat eel bones?
In Japan, yes: the backbones left over from preparing unagi are deep-fried into a crunchy snack called *hone senbei*, “bone crackers,” often eaten with sake. Elsewhere eel bones are usually discarded or used for stock.

The snack makes use of what would otherwise be waste: once the fillets have been lifted for grilling, the long chain of small vertebrae is left behind, and deep-frying turns it crisp. Japanese recipes apply the same bone-cracker treatment to the frames of other small fish.

A caution on morays. Large tropical morays sit near the top of reef food chains and can accumulate ciguatera toxins from the fish they eat. The giant moray is a recognised source of ciguatera poisoning, and eating its flesh, and especially its liver, can cause serious illness. That has nothing to do with the bones, but it is the main reason not to treat every eel as a food fish. Note too that the electric eel is not a true eel at all but a knifefish; see our [electric eel](/electric-eel/) page.

Why does an eel’s skeleton waste away before it spawns?
Because the eel stops eating and lives off its own body on the way to the spawning grounds, and its bones are one of the reserves it spends. A 2016 study of European eels found extensive bone loss during maturation and migration, carried out by bone-resorbing cells.

The European eel’s spawning journey runs about 5,000 km from European fresh waters across the North Atlantic to the Sargasso Sea. During that journey the eel matures sexually without feeding. A team led by Rolvien examined eel bones at different life stages and reported in *Proceedings of the Royal Society B* that the skeleton undergoes a remarkable transformation, with extensive bone loss mediated by multinucleated osteoclasts, the same type of bone-dissolving cell that remodels human bone. They found no sign of the alternative mechanisms seen in some other fish.

The puzzle was how an eel can dissolve its skeleton and still swim thousands of kilometres. The answer lies in two separate hard tissues in the eel’s backbone. The cellular bone acts as a mineral store that osteoclasts can break down, releasing minerals for the eel’s energy metabolism. Inside it, the mineralised sheath of the notochord, the stiff rod around which the backbone forms, is covered by an unmineralised layer that protects it from resorption, so the column keeps its mechanical stability. The authors concluded that the eel skeleton is structurally adapted to the double challenge of fasting and sexual development during the migration.

Conger eels go through something similar. Between about 5 and 15 years of age, as they mature, their reproductive organs enlarge while the skeleton loses mass and the teeth fall out; they then migrate to spawning areas in the Atlantic and Mediterranean, spawn once and die. An eel’s bones, in other words, are not a fixed scaffold but a resource it draws down at the end of its life.

What do eel ear bones tell scientists?
Age, growth and where the eel has lived. Eel otoliths, the small stones of calcium carbonate in the inner ear, lay down growth bands like tree rings, and their chemistry records whether the eel was in fresh, brackish or salt water at each stage of its life.

Otoliths are not true bones, but they are the hard parts that eel scientists value most. They grow throughout life by adding layers, usually faster in summer and slower in winter, and because they are not reabsorbed when the fish is starving they keep a continuous record. Counting the annual bands gives an age; in the larval stage, daily increments can be counted under a microscope, and Japanese researchers were describing daily rings in the otoliths of Japanese eel larvae by the late 1980s, opening a window on larval age and growth. Otolith reading is one way biologists know that European eels usually spend many years in continental waters before they mature: silver eels heading to sea are typically 6 to 12 years old for males and 10 to 20 years old for females, and captive eels have lived for more than 80 years.

The chemistry is even more revealing. Strontium substitutes for calcium as an otolith grows, and seawater contains much more strontium than most fresh water, so the ratio of strontium to calcium along an otolith tracks the salinity the eel lived in. Using this method, researchers led by Katsumi Tsukamoto and Takaomi Arai showed that eels are facultatively catadromous: some individuals never enter fresh water at all, spending their whole growth phase in the sea or in estuaries. A 2022 study in Norway used otolith chemistry to classify European eels as freshwater residents, seawater residents or habitat shifters, and a study of the tropical eel *Anguilla bicolor bicolor* found estuarine and marine residents among silver eels but no freshwater residents at all. The textbook picture of an eel that grows up in a river is only one of several life histories, and the evidence for that comes from the eel’s ear stones.

Otolith chemistry also has a commercial use. Trace-element fingerprints in the otoliths of Japanese eels differ between aquaculture farms, and in one study discriminant analysis assigned eels to their farm of origin with about 80 percent accuracy, a tool that could help trace eel through supply chains at a time when wild eel stocks are under heavy pressure.

What do eel bones tell archaeologists?
How much eel people ate, how big the eels were and how they were caught. Eel vertebrae are distinctive and survive well, so they turn up in large numbers in excavated rubbish pits, wells and floors.

A good example comes from the Castle Mall excavations in Norwich, England, reported by the fish-bone specialist A. Locker in an English Heritage Ancient Monuments Laboratory report of 1997. Eel was found in every period from Saxon to post-medieval times and in most of the sieved deposits, with 1,349 identified eel bones making up about 9 percent of the identified fish remains. Eel was most common in the earliest period, at around 17 percent of the fish bones, and the report notes that it was the only freshwater fish eaten in any quantity, a sign that local rivers were fished intensively for eels.

The same report shows how an eel’s anatomy shapes the archaeology. Vertebrae dominated the eel remains, partly because they survive burial and are recovered easily in sieves, while skull fragments were less common. Because one eel has so many more vertebrae than a herring or a cod, the analyst compared eel bone counts only with other eel counts across periods, not with other species, to avoid exaggerating eel’s importance. Measurements of skull bones suggested most of the eels were about 30 to 35 cm long, and the report suggested they may have been caught with spears and river traps as they migrated downstream to spawn, then eaten fresh or salted and pickled for storage.

How are moray eel bones different?
Morays have a second set of jaws in the throat that they launch forward to grab prey and drag it down, a system described in *Nature* in 2007 by Mehta and Wainwright.

Most bony fish have pharyngeal jaws, bony plates with teeth in the throat that process food. In morays these jaws sit farther back in the head, resemble the oral jaws, and can be shot forward into the mouth cavity to seize prey and pull it into the throat. Morays are the only animals known to use pharyngeal jaws to actively capture and restrain prey in this way. It is an adaptation for swallowing large prey in tight spaces, where a moray cannot rely on the suction feeding that most fish use.

Moray teeth and jaw bones also vary with diet. Fish-eating morays have long, pointed jaws and sharp teeth, and in the California moray some teeth in the roof of the mouth fold back as prey slides inward. Crab-eaters such as the zebra moray and species of *Echidna* have short, rounded jaws with blunt, molar-like teeth, a design that has evolved several times within the family, and the same pattern extends to the teeth on their pharyngeal jaws.

Common misconceptions about eel bones
“Eels are cartilaginous like sharks.” They are not. Sharks, rays and chimaeras have skeletons of cartilage; eels are bony, ray-finned fish. The leather sold as eelskin adds to the confusion, because it actually comes from the Pacific hagfish, a jawless animal sometimes called the slime eel, which is not an eel either.

“Eels have no bones because they are boneless when served.” Restaurant eel is boneless because it has been filleted. The skeleton is still there in the whole fish, and Japanese kitchens even turn it into a snack.

“All eels are equally bony.” Freshwater eels fillet cleanly; conger slices become bonier towards the tail; morays are tough and are rarely worth the risk where ciguatera occurs.

“An eel’s skeleton is permanent.” In migrating European eels and maturing congers the skeleton loses much of its mineral before spawning, while the core of the backbone is protected so the eel can keep swimming.

Frequently asked questions
Do eels have bones?

Yes. Eels are bony, ray-finned fish with a skull, jaws, gill arches, a long backbone and many fine fin rays.

How many bones are in an eel’s spine?

European eels average about 114 to 115 vertebrae (range about 104 to 120) and American eels about 107. The slender snipe eel has around 750.

Does unagi have bones?

Unagi is split and boned before grilling, so it is normally boneless; any tiny bones left behind soften in cooking.

Is conger eel bony?

Yes, more than freshwater eel. Slices from the belly near the head are nearly bone-free; slices from further down the body are bonier.

Can you eat eel bones?

In Japan, eel spines are deep-fried into crunchy crackers called hone senbei. Otherwise they are discarded or used for stock.

How do scientists tell an eel’s age?

By counting growth bands in its otoliths (ear stones). Otolith chemistry also shows whether it lived in fresh or salt water.

Why do eels lose bone before spawning?

Migrating eels stop feeding, and bone-resorbing cells release minerals from their bones while a protected core keeps the spine strong.

Are eels cartilaginous?

No. Sharks and rays are cartilaginous; eels are bony fish.

More eel answers

Eel Q&A

[Moray eels](/moray-eel-muraenidae/)
[Moray skeleton](/moray-eel-skeleton/)
[Is an eel a reptile?](/is-an-eel-a-reptile/)
[Are eels related to snakes?](/are-eels-related-to-snakes/)

Sources & further reading

- Boëtius, J. (1980). Atlantic *Anguilla*: a presentation of old and new data of total numbers of vertebrae with special reference to the occurrence of *Anguilla rostrata* in Europe. *Dana* 1: 93–112.
- Harding, E.F. (1985). On the homogeneity of the European eel population. *Dana* 4: 49–66.
- Naturalis Biodiversity Center, Fishes of the NE Atlantic and Mediterranean: *Anguilla anguilla*.
- Bigelow, H.B. & Schroeder, W.C. *Fishes of the Gulf of Maine*: American eel.
- Rolvien, T. et al. (2016). How the European eel (*Anguilla anguilla*) loses its skeletal framework across lifetime. *Proc. R. Soc. B* 283. doi:10.1098/rspb.2016.1550
- Mehta, R.S. & Wainwright, P.C. (2007). Raptorial jaws in the throat help moray eels swallow large prey. *Nature* 449. doi:10.1038/nature06062
- Tsukamoto, K. & Arai, T. (2001). Facultative catadromy of the eel *Anguilla japonica* between freshwater and seawater habitats. *Mar. Ecol. Prog. Ser.* 220. doi:10.3354/meps220265
- Bertolini, F. et al. (2022). Blood-based gene expression as non-lethal tool for inferring salinity-habitat history of European eel. *Sci. Rep.*; Arai, T. & Chino, N. (2022), *Heliyon*; Arai, T. & Kimura, S. (2022), *Biology*.
- Locker, A. (1997). The Saxon, medieval and post-medieval fish bones from excavations at Castle Mall, Norwich. Ancient Monuments Laboratory Report 85/97, English Heritage.
- Li, B. et al. (2021). Molecular mechanisms of intermuscular bone development in fish: a review. *Zoological Research*.
- Kabayaki and unagi preparation: Wikipedia; Just One Cookbook (hone senbei); Majorca Daily Bulletin (conger slices).

Continue reading
Related reading

[Eel Q&AEel SkeletonThe full anatomy.

](/eel-skeleton/)
[Eel Q&ADo Eels Have Scales?Smooth skin explained.

](/do-eels-have-scales/)
[EelsConger EelsBig marine eels with bonier flesh.

](/conger-eel-congridae/)
[Eel Q&AMoray Eel SkullTwo sets of jaws.

](/moray-eel-skull/)

BP

Last updated November 8, 2026
Written by
Blane Perun
Blane Perun has been exploring Earth’s oceans and marine life for over 25 years. Founder of TheSea.Org in 1999, underwater photographer, coral aquaculture pioneer, and explorer of 80+ countries.

[About Blane Perun →](/about-blane-perun/)