Puffer fish have a skeleton that’s quite unique. It’s a strange combination of a reduced skeleton, beak-like teeth, and spiky bones, called spines.
They’re able to expand into an incredible balloon thanks to a stomach that acts like a water balloon, and accordion-like folds in their skin that allow it to expand when inflated.
Spines
When puffers are threatened, they fill their bellies with water or air until they expand into a spherical shape that is two to three times larger than their normal size. This ability to “puff up” is one of the most important characteristics of puffer fishes, and is an essential defense mechanism in these aquatic predators.
Pufferfish are part of a family called Tetraodontiformes, which includes ocean sunfishes and triggerfishes. They’re a group of fish with many unique scale derivatives and skin ornaments, including feathers, hair, and the bizarre spines we see on their bodies.
Researchers have studied the development of these unique spines, and found that they’re shaped by conserved gene interactions that also drive the formation of other vertebrate skin appendages such as zebrafish scales, mouse hair, and chicken feathers. These findings, published July 25 in iScience, suggest that these genetic connections underlie the evolution of pufferfish spines and provide an explanation for the vast diversity of these structures in the ocean’s most unusual fishes.
In order to understand how pufferfish spinal development occurs, researchers examined the genetic code of a species that has not been well studied in the past: the Japanese grass pufferfish (Takifugu niphobles). They found that the same set of genes controls the development of the spiky skin structures that give these creatures their distinctive look.
By blocking particular genes that are classic markers of skin appendage development, the researchers were able to reduce the number of spines in the pufferfish and loosen the restriction on where they appear on the body. This is the first time that the genetics behind these spiky spines have been identified in an animal with such extreme variation.
The study is the latest in a series of discoveries that have revealed how diverse teleost skin ornaments can be. This research is an important step toward a better understanding of how animals use their skins to adapt to changing environments and climate changes, says Fraser.
The research team, led by Gareth Fraser of the University of Florida, used CRISPR-Cas9 and other genetic techniques to manipulate the genes that regulate the development of pufferfish spines. The results, which are published in iScience, show that these genes control the appearance of spines and that different morphological sets-ups of spines enable the fish to access new ecological niches as they adapt to climate change.
Ribs
The ribs of the puffer fish skeleton are quite interesting in themselves. They are a set of spiky bones that sit under the skin and expand outward like caltrops when the puffer fish inflates its belly. This means that when the fish doesn’t inflate, these spiky bone structures act as a kind of kevlar armor. They’re also pretty cool because they allow the puffer fish to float up in the water without requiring a large amount of energy from their muscles.
The reason why the ribs are spiky is because they’re supposed to protect the puffer fish from predators. The ribs are actually connected by a hinge, so they can easily change position when the puffer fish needs to inflate its belly. And the ribs are also meant to prevent other fish from grabbing them and stuffing them into their mouths!
However, these ribs aren’t the only thing that makes the puffer fish so special. They’re also the second most poisonous vertebrate in the world. Puffer fish contain a toxic substance called tetrodotoxin that can kill people who eat them if they’re not properly cooked or prepared.
There are 120 species of pufferfish that live in tropical waters all over the world. And they all share one trait that makes them so scary: when threatened, these fish can rapidly fill their belly with air or water and inflate to twice or three times their normal size.
These strange and colorful fish are a member of an order of tropical fish known as Tetraodontidae, which includes triggerfish and tripodfish. Using the evolutionary tree below, you can trace how the ancestors of these creatures came to gain the ability to inflate themselves.
The pufferfish’s ancestors evolved from triggerfish, which had long been able to inflate their bodies. But it was only when the pufferfish’s ancestors moved on from triggerfish that they branched away from their relatives to become more distinct.
Unlike triggerfish, which have many vertebrae and a pelvic appendage, puffer fish have a very simple skeletal structure. In fact, their skeleton is much more like that of a zebrafish. In fact, they have even lost their pelvic appendage!
Pelvic Fins
Puffer fishes are among the most diverse fish species on Earth, ranging in size from less than an inch long (2.5 cm) to some of the largest fishes in the ocean that can weigh up to 6,000 lbs (2,721 kg) and reach 10 ft (3 m) in length. They live in marine habitats from the coasts and reefs to open pelagic waters and deep ocean.
They are members of the order Tetraodontiformes, which includes 447 species in ten families. The group is best known for their ability to inflate their bodies when threatened by predators. They can also develop a variety of other antipredator adaptations such as being covered with stiff, inflexible armored plates or having powerful toxins that are capable of killing an entire family of predators.
The skeletal structure of a puffer fish’s pelvic fin is very similar to that of other teleosts. Most teleosts have four proximal radials and no mesocoracoid in their pectoral fins. However, there are some exceptional forms that have only two proximal radials and no pectoral rays, such as angler (Lophius piscatorius) and the African mouthbrooding cichlid (Astatotilapia burtoni).
These skeleton components can be found in many of the different vertebrates, including birds, reptiles, amphibians, mammals, insects and echinoderms. In a variety of clades, the pectoral fin skeleton is often accompanied by a pair of ribs that support the head and jaw.
In some cases, the ribs are fused together into one bone, which is known as an occipital bone. In other cases, the ribs are separated and each rib has a unique shape and size.
This unique morphology is sometimes thought to be a result of the reduced complexity of the Hox complexes that are present in puffer fishes. In fact, a small Japanese pufferfish named Takifugu rubripes has been shown to have one of the smallest known vertebrate genomes in existence.
Pelvic fins are also very important in some marine organisms, such as sea anemones. These fishes are able to inflate their bodies when they are stressed or when they are facing danger, using the tissue of their pelvic fins as an air sac that can expand up to 50-100-fold depending on the species. This is important because it can allow the animal to survive in situations where it would otherwise be fatal.
Cranium
Unlike most fish, pufferfish have a relatively rigid skeleton and cannot bend much in the middle. They also lack a true stomach and must develop the ability to inflate to survive.
The cranium is a complex network of bones that form the skull and face of the animal. The skulls of jawless fishes and sharks are formed from only loosely connected bones, while the endocranium of cartilaginous fishes has additional dermal bone, forming a more coherent roof around the skull. The skull is separated from the upper and lower jaws by a chin that is formed from the front of the lower jaw.
A number of different muscles are used to actuate the cranial functions of a fish, but the most important is the LO muscle which opens the mouth during normal breathing and coughing or water blowing. When the fish inflates, the LO muscle is very much reduced in activity and the mouth closes to prevent water from escaping out of the mouth.
There are a few other muscles that help the pufferfish inflate, but their role is rather limited. In addition to the LO muscle, the PH and PP muscles are involved, but their role is less distinct.
When a pufferfish isn’t inflated, the spiky bones of its skeleton form a hard armor over its skin. These ‘caltrops’ are actually just layered over each other to form a very stiff shield that helps prevent predators from entering the animal and getting their mouths on it!
Pufferfish skeletons are very unique and fascinating. It was really cool to make a pet memorial for a pufferfish named Sushi!
They range in size from the dwarf pufferfish, which is only 1 inch long, to the giant pufferfish, which can grow up to 2 feet long. The smallest species of pufferfish are scaleless and often have rough or spiky skin, while the largest have thick, smooth skin that can be difficult to distinguish from the rest of the fish.
Some of these fish are highly toxic to humans. The deadly neurotoxin tetrodotoxin is found in many parts of the body of pufferfish, and eating enough of it can cause nausea, vomiting, and respiratory failure. In some regions of Japan, the ovaries of pufferfish are salted and then soaked in rice bran to detoxify the poison before being eaten. This process, called nukazuke, requires re-salting the ovaries several times before the toxin is completely eliminated.