Why Do Pufferfish Have Square Bodies? Exploring the Unique Geometry of Aquatic Curiosities
What no one expected is that, despite its seemingly slow appearance, the golden chest pufferfish is remarkably agile.
The black-spotted yellow fish, which resembles a square box, is scientifically known as Ostracion cubicus, commonly referred to as the round-backed puffer or the golden box puffer. They are primarily found in the coral reefs of the Pacific, Indian Ocean, and the southeastern Atlantic Ocean. Their diet consists mainly of small prey like small worms, crustaceans, mollusks, and small fish, as well as organic debris on the reef’s surface.
The fish’s body is bright yellow with round black spots covering it, giving it the appearance of a box with black spots on a yellow background. This coloration serves as a warning to potential predators, as the golden chest puffer is a solitary and shy creature.
When threatened or attacked, the skin of the golden chest pufferfish releases a distinctive neurotoxin called Ostracitoxin. Many people have attempted to keep them in aquariums with little success because the toxins they release can harm other fish in the tank when kept in a relatively closed environment.
Most fish have soft, elongated bodies adapted to their aquatic environment, enabling them to swim freely. However, the golden chest pufferfish stands out with its hard, box-shaped skeleton, a stark departure from the typical fish body structure. This unique shape raises questions about its evolution. How can it swim with such a boxy body?
Surprisingly, the golden chest puffer is incredibly agile, considered one of the fastest fish in the reef. In 2002, a team of researchers used 3D-printed models of pufferfish to study how water flows around their bodies. They discovered that when water hits the pufferfish, small eddies form near their shells, helping stabilize their movement.
This ingenious survival technique minimizes water flow disturbance and maintains stability in fast-moving waters. Finally, humans have found an explanation for the evolution of the pufferfish’s peculiar shape, especially in the case of the golden box puffer.
However, researchers may have overlooked one crucial detail. While eddy currents around the pufferfish’s skeleton provide stability, they also make the fish reliant on the vortex around their bodies. So, is it challenging for them to change direction when a predator suddenly attacks?
Observations by research staff reveal that the golden chest pufferfish is highly flexible. When in danger, it swiftly turns around and swims into the reef to escape. Research by S. Van Wassenbergh et al. in 2015 challenged earlier theories about whirlpools, arguing that the influence of these eddies is countered by the moment of force generated in front of the box-shaped skeleton. The pufferfish cannot maintain a stable position but are easily “turned over.”
The reason for the golden chest puffer’s agility lies in a combination of its aerodynamically unstable body and the movement of its fins. Furthermore, they do not need to swim long distances and possess venom and “armor,” making agility a more favorable evolutionary choice over speed.
You might wonder how the fish with such a boxy body typically swim. If you’ve ever watched fish in motion, you’ll notice they all move in a coordinated way, involving the tail, body, and the coordination of their fins.
The pectoral and pelvic fins help the fish maintain balance in the water, unlike other types of fins. The pectoral fins are horizontal, shaking water up and down during movement to help the fish control its vertical position. The dorsal and caudal fins keep the fish upright in the water, similar to the keel of a sailboat.
The tail fin not only provides power for swimming but also helps the fish change its direction. When the caudal fin swings left, the fish moves left, and when it swings right, the fish moves right. However, due to differences in habitat and behavior, the function and shape of fins have also evolved accordingly over a long period.
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