Fish Vertebrae: What Is It And What Are The Causes

One of the most prominent features of the human body is the presence of the spinal column, which is formed by bones called vertebrae.

However, some underlying diseases can lead to concavity in the vertebrae of humans. This condition is known as fish vertebrae, codfish vertebrae, or fish mouth vertebrae.

The risk factors which result in fish vertebrae are sickle cell anemia, osteoporosis, osteomalacia, and so on. Overall, some of the diseases which cause weakening or softening of bones may result in this condition.

The main feature of fish vertebrae is the transformation of some of the vertebral bones into a biconcave shape. This biconcave shape is similar to the spine of fishes.

The diagnosis of fish vertebrae is made through evaluating one's symptoms and, more successfully, through radiographic imaging. Treatment of the main cause of fish vertebrae aids the patients in better managing their condition.

To learn more about fish vertebrae, keep reading! You can also check out do fish have eyelids and do fish have livers. 

What are fish vertebrae?

In humans, the vertebrae may sometimes look like the vertebrae of a fish, and this is known as fish vertebrae. Other names for this abnormality include codfish vertebrae and fish mouth vertebrae.

In a person with codfish vertebrae, the vertebral bodies have a concave depression on their upper and lower sides. This smooth deformity leads to biconcave vertebrae in people.

In sickle cell disease, the bone scans have revealed the biconcave shape is formed due to the compression of the vertebral bodies by the adjacent intervertebral discs and the depression of the vertebral end-plates.

Fuller Albright, an American endocrinologist, was the one who came up with the term 'fish vertebrae'. The naming was done based on the fact that the biconcavity of the human vertebrae was similar to the appearance of fish vertebrae.

Much later, Fuller Albright and another American endocrinologist by the name of Edward Reifenstein used codfish vertebra to compare the shape of vertebral bodies in women with osteoporosis.

This gave birth to the name 'codfish vertebrae'.

The name 'fish mouth' was given due to the similarity of this kind of vertebral growth to that of the mouth of a fish. However, many researchers have established that the fish vertebra bears the closest resemblance to the tuna spine or salmon spine instead of the mouth of a fish.

What causes fish vertebrae?

A number of reasons have been attributed to fish vertebrae. From diseases related to the bone to genetic disorders, the codfish vertebrae cover a wide range of etiologies.

Sickle cell anemia- The sickle cell trait is an inherited blood condition that results in the formation of red blood cells of a sickle shape instead of its usual shape. Unfortunately, sickle cell disease has a connection with fish vertebrae.

The effect of sickle cell anemia on the skeletal system, including thinning and softening of bones and marrow hyperplasia, makes this disorder a risk factor for fish vertebrae.

In a patient, it was observed that the fish vertebra sign manifested in the lumbar region and appeared as biconcave lumbar vertebrae. This was further characterized by bone softening and an exaggeration of the normal concavity of the vertebral bodies.

This sort of disturbance to vertebral growth has been attributed to micro bone infarctions. In this case, the bone infarction took place in the central region of the vertebral growth plates.

The bone infarcts were caused by the lack of blood supply to that region. Acute infarction of the long bones in sickle cell not only results in avascular necrosis but is one of the underlying causes of fish vertebrae.

Osteoporosis- A diffuse weakening of bones is one of the prime causes of the fish vertebra sign in humans. This kind of weakening is caused by osteoporosis.

Osteoporosis literally translates to 'porous bones' and is a kind of bone disorder that increases one's risk of vertebral fractures. A less severe form of osteoporosis may result in certain joint disorders.

One of the clinical features of osteoporosis is it usually affects a single vertebral body. The superior and inferior surfaces of the vertebral body get the characteristic depression, which is the main feature of the fish vertebra.

Apart from these, a number of other diseases also result in the abnormal concavity of the human vertebrae. Some of them are osteomalacia, homocystinuria, osteogenesis imperfecta, Paget's disease, and hereditary spherocytosis.

Fish Vertebrae Identification

A number of clinical manifestations are associated with codfish vertebrae, and these symptoms can be used to identify the presence of a single fish vertebra or multiple fish vertebrae in anyone. Additionally, spinal X-ray also lets doctors and medical practitioners understand the issue and provide effective medical treatment with the appropriate internal medicine.

Lumbar pain and bilateral lower limb pains maybe some of the signs used to identify fish vertebrae. However, more concrete evidence can be collected through radiological imaging. Needless to say, the main way to identify fish vertebrae is through the appearance of the biconcave vertebral bodies.

However, this biconcavity presents itself differently, depending on the cause of the fish vertebrae. For instance, in sickle cell disease, the posterior, anterior, and lateral sides of the spine have bone softening in addition to its biconcave appearance.

In the case of osteoporosis, usually, a single vertebra is affected, and this codfish vertebra has an irregular biconcave appearance. Another defining feature of the codfish vertebra caused due to osteoporosis is the presence of subchondral bones on the upper and lower side of the vertebra that has the deformity.

Care should be taken not to confuse flat vertebrae or Gaucher disease with fish vertebrae. While flat vertebrae are the result of the compression of the entire vertebral surface, Gaucher disease results in an enlarged bone marrow space.

How many vertebrae does a fish have?

Fishes are a part of the subphylum Vertebrata and are characterized by the presence of a vertebral column. The vertebral column in fishes has centrum, vertebral arches, and multiple processes.

While the centrum is the central spine, the vertebral arches arise from the centrum. The processes arise from both the centrum and the vertebral arches. In comparison to the flat centrum found in mammals, the centrum of a fish is concave.

Interestingly, the primitive lampreys do not have the kind of vertebral bodies which are expected to be found in vertebrates. However, they do have vertebral arches. Overall, there are varied differences in the skeletal system of fishes, and this includes the number of vertebrae possessed by a species.

The commonly known fish Rohu, with the scientific name Labeo rohita, has 37-38 vertebrae. The entire vertebral column is ossified in this species, and the centrum is concave on both ends.

Their entire vertebral column can be distinguished into trunk vertebrae and caudal vertebrae. The trunk vertebrae are composed of 21 bones, while the caudal vertebrae have 16-17 bones. Both these vertebral regions have neural arches and postzygapophyses.

Other fishes like the common carp and goldfish have 33-36 and 26-28 vertebrae, respectively. The famous tuna fish, which is usually available in canned form, has 39 vertebrae making up its spinal column.

Belonging to the group of cartilaginous fishes, sharks are quite well-known. In massive white sharks, the number of vertebrae in the skeletal system is usually between 170-187.

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