Golden Ark Puffer Fish - Fish with a strange square shape

Despite possessing a bulky body, the yellow puffer fish still swim as fast as a shot to catch prey using the caudal fin.  

The golden pufferfish has a square rectangular body like a plastic box with fins attached. Despite their clumsy appearance, this fish can wriggle through the corners of the coral reef and catch shrimp. Pim Boute, a doctoral student at Wageningen University in the Netherlands, and his colleagues discovered how pufferfishes use their caudal fins to navigate in research published on April 8 on the Royal Society Open Science page.

Puffer fish with box-shaped body. (Photo: NYT).

Most fish from minnows to sharks have malleable bodies, helping them to follow the movement of the water. But the puffer fish has hard armor linked together into a box around the body, acting as armor to protect them from predators but limited flexibility. So when you want to move, puffer fish only use fins, according to Boute.

Based on previous studies as well as underwater observations, Boute speculates that the  caudal fin is an important factor in creating undulating motion on the horizontal plane. To test this hypothesis, Boute and colleagues used a plastic 3D model of the tailless puffer fish. They dropped the model into the tank, used a thin rod to fix it in place and pumped the water over like it was when a real fish was swimming while a sensor measures the rotation of a fake fish.

The team repeated the process several times, each time changing the angle of the fake fish against the water. They then carried out the same experiment with a model of caudal fins. They try the fins in a variety of positions, such as spreading, straightening or turning left or right.

The researchers found that without the caudal fin, the puffer fish relies on the jostling water. But the wide-spread tail makes it stable regardless of the body's angle to the water. Meanwhile, the tail is closed to allow the fish to cope with the effects of the water coming from many different angles. This shows that by spreading, closing or bending the tail, the puffer fish can control body movement at will.

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