Scoliosis, the sideways curvature of the spine, affects far more than just humans. Fish, dogs, cattle, chickens, primates, and reptiles all develop spinal curves that mirror the condition diagnosed in people. The range of affected species has surprised researchers for decades, partly because it upends the old assumption that scoliosis is a consequence of walking upright. Studying these animals has done more than catalog a curiosity; it has reshaped what scientists understand about why spines curve in the first place.
Why Scoliosis Is Not a Human Problem
For a long time, a popular explanation for idiopathic scoliosis (the kind that shows up in adolescents without an obvious cause) was that it had something to do with bipedalism. Balancing a tall, upright spine on two legs seemed like a recipe for things to go wrong. But the sheer number of quadrupeds and aquatic animals that develop scoliosis makes that explanation hard to sustain. Research on guppies, for instance, found that the primary loading on a fish’s spine runs along the same head-to-tail axis as it does in a standing human, just driven by water resistance and tail-beat forces instead of gravity. The way vertebrae compress on the concave side of a curve in guppies closely resembles what happens in human idiopathic scoliosis.1PubMed Central. Idiopathic-type scoliosis is not exclusive to bipedalism Biomechanical studies on goat spines reinforce this point. The quadruped spine is loaded mainly by axial compression along its length, just like the human spine, and the vertebral bone density of four-legged animals is actually higher than ours, suggesting they sustain even greater compressive stresses.2PubMed Central. The use of a quadruped as an in vivo model for the study of the spine – biomechanical considerations
The upshot is straightforward: scoliosis is not a penalty for standing upright. The fundamental mechanics of how vertebrae bear loads are surprisingly similar across species, which is why the condition turns up in animals that swim, walk on four legs, fly, or slither.
Fish and Aquatic Species
Fish are some of the most commonly documented animals with scoliosis, in part because millions are bred in aquaculture settings where spinal deformities are impossible to miss. Farmed Atlantic salmon develop spinal curves so frequently that the condition has its own set of informal names: broken back syndrome, curvy back disease, and short tails. Intensive farming conditions are heavily implicated, and deformities translate directly into production losses for the industry.3PubMed Central. Spinal deformities in farmed Atlantic salmon
Water temperature plays a measurable role. In experiments with golden pompano, the rate of spinal malformation climbed significantly as rearing temperatures rose from 26 °C to 32 °C, with the highest deformity rate at the warmest temperature.4Aquaculture Reports. Impact of temperature on survival and spinal development of golden pompano Trachinotus ovatus (Linnaeus 1758) For fish farmers, this is a practical headache: warming water in climate-stressed environments can directly increase the share of fish that grow up with crooked spines.
Parasites are another trigger. Flathead fish found with pronounced scoliosis and kyphosis (an abnormal forward-rounding of the spine) turned out to have tiny cysts sitting on top of their brains, concentrated over the optic lobe and cerebellum. The culprit was a Myxobolus parasite, identified through DNA sequencing, whose cysts apparently disrupted the nervous system enough to warp the spine.5PubMed Central. Scoliosis and kyphosis in blue-spotted and marbled flathead fish associated with a Myxobolus acanthogobii-like parasite And then there are toxins: exposure to the organochlorine pesticide Kepone causes scoliosis in sheepshead minnows, along with muscle hemorrhage and fractured vertebrae. The nervous system appears to be the primary target, with the spinal curvature arising as a secondary effect of the poisoning.6PubMed. Kepone-induced scoliosis and its histological consequences in fish
The variety of causes in fish alone (genetics, water temperature, parasites, chemical contamination) hints at something important about scoliosis across all species: it is not one disease with one cause. It is an outcome that many different disruptions can produce.
Dogs and Livestock
Among companion animals, certain dog breeds stand out. French Bulldogs, English Bulldogs, and Pugs are predisposed to a suite of vertebral malformations including hemivertebra (a wedge-shaped vertebra that throws the spine off-center), spinal canal narrowing, and abnormalities in the joints between vertebrae.7PubMed. Vertebral and spinal malformations in small brachycephalic dog breeds: Current knowledge and remaining questions Hemivertebrae are remarkably common in these breeds. A study examining 160 dogs with at least one thoracic hemivertebra found that many of the animals had been scanned for reasons completely unrelated to spinal problems, meaning the malformation was an incidental finding in otherwise healthy-seeming dogs.8Journal of Veterinary Internal Medicine. Comparison of signalment and computed tomography findings in French Bulldogs, Pugs, and English Bulldogs with and without clinical signs associated with thoracic hemivertebra That said, severe kyphosis combined with hemivertebra, especially in Pugs, does increase the chance of neurological symptoms like hind-limb weakness or incontinence.
Cattle deal with their own version. When pregnant cows graze on certain lupine plants during a critical window of gestation (roughly days 40 to 70), the toxic alkaloids in those plants can cause severe skeletal birth defects in calves, a condition ranchers call “crooked calf syndrome.” Continuous grazing on teratogenic lupine for as little as 30 days during that window is enough to produce dramatic spinal and limb deformities in the offspring.9PubMed Central. Lupine-induced crooked calf syndrome: mitigation through intermittent grazing management of cattle The primary culprit is an alkaloid called anagyrine, though related compounds like ammodendrine also play a role.10Journal of Animal Science. The effect of body condition on serum concentrations of two teratogenic alkaloids (anagyrine and ammodendrine) from lupines (Lupinus species) that cause crooked calf disease Managing grazing schedules to keep pregnant cows away from lupine patches during that vulnerable period is the main prevention strategy.
Beyond dogs and cattle, captive-bred rhesus macaques have been documented with true scoliosis that develops in an analogous way to the human condition, providing further evidence that four-legged animals are not protected from spinal curvature by their posture.11PubMed. Preliminary studies of neurosensory and cardiopulmonary health compromise in captive-bred Rhesus macaques (Macaca mulatta) suffering scoliosis
Birds and Reptiles
Broiler chickens, bred for rapid growth, develop a cervical form of scoliosis and torticollis (a twisted neck) that appears to stem from abnormal bone remodeling in the neck vertebrae. The pathology involves excessive activity of the cells that break down bone, essentially weakening and reshaping the vertebrae until the cervical spine curves and twists.12PubMed Central. Cervical scoliosis and torticollis: a novel skeletal anomaly in broiler chickens In a bird bred to grow as fast as possible, the skeleton sometimes cannot keep pace with the body’s demands.
Reptiles develop scoliosis too, though published reports tend to be scattered across case studies. Turtles and tortoises are the most frequently reported group, likely because their shells make spinal abnormalities easy to spot and because they attract more research attention than snakes or lizards. The condition appears across all major reptile lineages, and while it remains uncommon in wild populations, its presence in the fossil record proves it is nothing new.
The oldest known case of congenital scoliosis in an amniote (a land-adapted vertebrate) comes from a mesosaurid, a small aquatic reptile that lived during the early Permian period, roughly 280 million years ago. CT scanning of the fossil revealed a wedge-shaped hemivertebra jammed between its neighbors, misshaping the spinal canal without fully blocking it. The number of ribs on each side matched the number of vertebrae, a detail that confirms the deformity was congenital rather than caused by injury or disease.13PLoS ONE. New tomographic contribution to characterizing mesosaurid congenital scoliosis Scoliosis, in other words, has been part of vertebrate life since long before anything walked upright.
How Zebrafish Changed the Understanding of Human Scoliosis
Zebrafish have become the most important animal model for studying scoliosis, and the discoveries that have come out of zebrafish labs over the past decade are genuinely striking. The fish are small, transparent in early life, easy to breed in large numbers, and share enough genetic overlap with humans that findings in zebrafish often point directly at mechanisms relevant to people.
The breakthrough finding centered on cerebrospinal fluid (CSF) flow. Researchers studying zebrafish with a mutation in a gene called ptk7 found that the fish developed scoliosis that closely resembled human idiopathic scoliosis. When they looked more closely, the problem was in the tiny hair-like cilia that line the brain and spinal cord cavities. These cilia normally beat in coordinated waves to push CSF through the central nervous system. In the ptk7 mutant fish, the cilia did not develop properly, CSF flow was disrupted, and scoliosis followed. Crucially, when the researchers genetically restored normal cilia function in just the cell lineages responsible for CSF movement, scoliosis was prevented. And when they knocked out several other, unrelated cilia-motility genes, those fish also developed scoliosis.14PubMed Central. Zebrafish models of idiopathic scoliosis link cerebrospinal fluid flow defects to spine curvature The implication was that disrupted CSF flow is not just correlated with scoliosis but plays a causal role in its development.
A separate zebrafish mutant, carrying a temperature-sensitive mutation in a different cilia gene called cfap298, reinforced the point. When these fish were shifted from a cooler to a warmer environment (which inactivated their cilia), about 63% developed three-dimensional spinal deformity with curves averaging around 42 degrees in the frontal plane. The deformity closely matched the characteristics seen in human adolescent idiopathic scoliosis patients.15Scientific Reports. The orthopedic characterization of cfap298tm304 mutants validate zebrafish to faithfully model human AIS These zebrafish experiments have opened up a line of research into whether therapies targeting CSF dynamics could one day prevent scoliosis progression in children, an idea that would have seemed far-fetched before tiny fish pointed toward the mechanism.
What Chickens Taught Researchers About Melatonin and the Spine
Before zebrafish took center stage, chickens were the go-to experimental animal for scoliosis research, and the experiments were revelatory in their own right. The key finding was that removing the pineal gland from young chicks (a procedure called pinealectomy) reliably produced scoliosis. In one study, scoliosis developed in 75% of pinealectomized chickens, compared to 19% of unoperated controls. Lower blood melatonin levels were strongly associated with developing the condition.16PubMed Central. Pinealectomy in the chicken: a good model of scoliosis?
A follow-up experiment made the connection to melatonin even more explicit. Pinealectomized chicks given melatonin supplements developed scoliosis at dramatically lower rates: only 6 out of 30 treated chicks, compared to all 30 in the untreated control group. The chicks that did develop scoliosis despite melatonin treatment had milder curves. Blood melatonin levels were consistently lower in chickens with scoliosis than in those without.17The Journal of Bone and Joint Surgery. British volume. Role of melatonin deficiency in the development of scoliosis in pinealectomised chickens The proposed explanation was that melatonin deficiency disrupts the normally symmetrical growth of the proprioceptive system, the sensory network that helps the body sense its own position, including the paraspinal muscles and spine.
Later work tried to refine the model by transplanting pineal gland tissue back into pinealectomized chicks. The transplant partially restored melatonin production, and the rate of scoliosis dropped somewhat compared to pinealectomized chicks without transplants (about 50% versus 58%), though the difference was modest.18PubMed Central. The effects of pineal gland transplantation on the production of spinal deformity and serum melatonin level following pinealectomy in the chicken The chicken model has its limitations. Even sham surgery produced scoliosis in over a third of chickens in one study, raising questions about how much of the effect is purely from melatonin loss versus surgical stress.19PubMed Central. Pinealectomy in the chicken: a good model of scoliosis? Still, the chicken experiments were among the first to demonstrate that a hormonal disruption could trigger scoliosis in an animal, and they remain an important piece of the larger puzzle.
Common Misconceptions About Animal Scoliosis
One widespread misunderstanding is that wild animals with scoliosis cannot survive. While severe curvature certainly impairs mobility and, in aquatic species, swimming efficiency, many animals live full lifespans with mild to moderate spinal curves. The mesosaurid fossil mentioned earlier had a continuous spinal canal despite its deformity, meaning its spinal cord was likely uncompressed. In dogs, many brachycephalic breeds carry hemivertebrae for years without any visible symptoms. The question is not whether scoliosis exists in a given species but how severe it is and what compensatory adaptations the animal’s body can make.
Another misconception is that scoliosis in animals is always caused by inbreeding or poor husbandry. While both can increase the risk, the condition arises through a strikingly wide array of pathways. Genetic mutations, parasitic infections, chemical toxins, nutritional deficiencies, abnormal water temperatures, and hormonal disruptions can all produce spinal curvature. In many wild populations, scoliosis appears at low but consistent rates without any human-caused trigger. It is, to some degree, an inherent vulnerability of the vertebrate body plan itself.
What This Means for Pet Owners and Farmers
If you own a French Bulldog, Pug, or English Bulldog, the odds are reasonably high that your dog has at least one hemivertebra on imaging, even if it never shows symptoms. Veterinary guidance generally advises monitoring rather than intervention unless neurological signs develop. The breeds’ extreme popularity has outpaced the scientific understanding of when these spinal abnormalities cross the line from anatomical quirk to clinical problem. Severe kyphosis in Pugs, in particular, warrants closer attention.20PubMed. Vertebral and spinal malformations in small brachycephalic dog breeds: Current knowledge and remaining questions
For cattle ranchers in the western United States and other regions where lupine species grow wild, crooked calf syndrome remains a real economic concern. The prevention approach is management-based: keep pregnant cows off lupine-heavy pastures during the first trimester, especially between days 40 and 70 of gestation.21PubMed Central. Lupine-induced crooked calf syndrome: mitigation through intermittent grazing management of cattle Intermittent grazing, where cattle are rotated through lupine-containing pastures for only short windows, can substantially reduce the risk.
In aquaculture, spinal deformity rates are monitored as a quality and welfare metric. Maintaining stable, species-appropriate water temperatures is one of the most controllable factors. As water temperatures in many farming regions creep upward due to climate change, the connection between warmth and spinal malformation in fish like golden pompano is not just academic.22Aquaculture Reports. Impact of temperature on survival and spinal development of golden pompano Trachinotus ovatus (Linnaeus 1758) Farms that can control water temperature have a direct lever to pull; those relying on ambient conditions may face growing rates of deformity in the years ahead.