Science Spotlight: Fish, Swim Bladders and Boyle's Law

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Article by Lauren Farrar

Scientists at the California Academy of Sciences have recently engineered a device that allows them to collect newly-discovered fish species from the ocean’s “twilight zone” and safely bring them up to the surface to study. Prior to this invention, it was difficult for scientists to study fish in this region because many fish can’t handle the rapid change in pressure they experience when being transported to the surface.

In water, pressure increases with depth. When you are submerged in a body of water, like the ocean, you experience pressure from the force of the water surrounding you. At the surface, the pressure from the water is the same as the pressure from the air. However, as you descend, pressure increases because there is more water above you. The weight from all that water creates a greater force pushing against you, therefore you experience greater pressure.

Why does this pressure matter for fish?

Many fish have a gas-filled organ, called a “swim bladder,” that helps them maintain their buoyancy. Because the swim bladder is filled with gas, it’s hard for fish to handle quick changes in pressure. Boyle’s Law explains the relationship between pressure and volume of a gas. As pressure increases, the volume of a gas decreases; and, as pressure decreases, the volume of a gas increases.

So, if scientists bring fish from the twilight zone—where the pressure is high—to the surface, where the pressure is lower, the volume of the gases in the swim bladder increases causing the swim bladder to expand. The swim bladder can expand so much that it can crush other vital organs inside the fish and cause the fish to die.

In the above video, Matt Wandell, a biologist at the California Academy of Sciences, demonstrates how pressure affects a fish’s swim bladder. Wandell was among one of the scientists that helped engineer a portable fish decompression chamber to safely bring fish up from the twilight zone. This device maintains high pressures while fish ascend to the surface. Once at the surface, the chamber is hooked up to a pump that slowly decreases the pressure in the chamber. This allows enough time for the fish to regulate the gas in their swim bladders and adjust to life at a lower pressure.

This Science Spotlight is a companion video to Bringing Fish Up from the Deep and is part of our Engineering Is: Bringing Fish Up from the Deep e-book. The e-book explores the science and engineering principles behind the California Academy of Sciences’ portable decompression chamber, and includes videos, interactives and media making opportunities. You can find our other e-books at kqed.org/ebooks.