Cowfish fact
Cowfish have a net negative current resistence.
Their box-like shape allows water to flow smoothly over the part of their body facing the direction the current is coming from while causing it to circulate on the reverse side of their body.
This creates and area of low pressure at the part of the body the current comes from and high pressure at the opposite side.
The overall effect means that the force of the water itself pulls the fish towards the current's origin.
This has 2 evolutionary advantages.
First of all, small cuttlefish that would normal use a blast of water to deter or deflect a predator only draw the cowfish closer where the fish can take a glancing bite.
Secondly, certain predator fish such as stonefish, blobfish and frogfish use a suction gulp to catch small fish but when used against a cowfish this instead blows the prey away from them.
This strange aquadynamic effect works no matter what direction the cowfish is actually facing and the cowfish can simply swallow water to slightly round out its shape to create the reverse effect and prevent itself from being washed away.
This is why no matter the currents cowfish will appear to almost hover in place as they are hardly moved much by strong currents.
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