I caught my first fish when I was 12, sitting in a small boat with my grandpa on a lake in eastern Washington. Something took my bait, and I nervously pulled up a little perch.

I should have felt proud, but watching it lie there in the boat, gasping, I was overcome with guilt. Grandpa, seeing the stricken look on my face, gently picked up the hapless fish, removed the hook from its mouth with surgical precision, and tossed it back in the water, grinning. What an understanding human being!

In the meantime, I’d had a close look at the perch’s gills; they were both startling and fascinating, but a little gruesome (I think today’s term is “gross”). The whole sieve-like mechanism resembled a bunch of curved parallel combs colored a glistening scarlet, opening and collapsing rhythmically as the fish tried in vain to breathe while out of water. I’ve since learned more about this amazing process. Like all animals, fish breathe oxygen and exhale carbon dioxide. Seawater contains plenty of oxygen but, of course, it’s in a dissolved state.

So, how do our finny friends make use of oxygen that’s in a solution? If you’ve visited an aquarium or gone snorkeling, you may have watched fish open and close their mouths continuously whether they’re swimming or stationary. This pumping action pulls water over the gills, after which the gill cover closes and momentarily traps the water inside.

At the risk of biological overload: a fish’s feathery gills (those little red combs mentioned above) are full of blood vessels. As water passes through, dissolved oxygen is taken up by the blood and makes its way to the fish’s cells. The unneeded carbon dioxide is expelled. That’s at least one thing we have in common with these water-dwellers: oxygen in, carbon dioxide out.

Now, let’s switch gears. If this is how fish get their oxygen, why do our resident marine “big guys” (whales, dolphins and orcas, for example) need to surface to breathe? It’s because they’re not fish, but mammals, just like us. They give birth to live babies instead of laying eggs like fish do. They’re warm-blooded and have lungs like ours. They may spend their lives in water, but they’re actually air-breathers. Surfacing periodically, they suck air in through a “nose,” an opening on top of the head (not a convenient location for us, but perfect for them).

Once their lungs have extracted the oxygen, the water is blown out through the same opening, resembling a column of steam. More than once, while on a Puget Sound ferry, I’ve watched this process (along with all my fellow passengers as we dashed to one side of the boat, causing it to list to starboard).

Switching gears again: The sea floors all around us fairly percolate with life — oodles of marine critters, like sea stars, oysters and spiky urchins, for example. How do they breathe? Again, thank those glorious gills. For these non-fish animals, the gills take some rather bizarre forms. Sea stars, for example, may appear as five-armed, unmoving lumps on the bottom, but they’re definitely not comatose and they have to breathe. First, a little sieve-like hole on top of the star pulls water inside, where it’s routed through the body via a complex canal system.

On the underside of the star are thousands of tiny “tube feet,” they’re part of this plumbing apparatus but they also move the animal across the bottom (albeit very, very slowly) as it searches for clams and other shellfish to pry open and dine upon. More important, inside those little squiggly appendages full of water, carbon dioxide is eliminated and oxygen is absorbed. Every marine species has its own custom equipment for breathing … Nature has invented endless gadgets to keep its creatures alive.

Whether our water-dwelling neighbors breathe air directly or let gills do the work, a specter hangs over them all: pollution affects them just like inhaled smoke and other airborne toxins affect us. Poisons from metals, pesticides and other poisons, introduced by us into seas and rivers, wind up in an animal’s muscle tissue and some of its organs, leading to mortality. Examples here in Kitsap County: pollutants in our streams, where adjacent development contaminates the water and sometimes kills returning salmon before they can spawn.

Until we clean up our waters, the cards are certainly stacked against our fresh and salt water neighbors.

— Nancy Sefton is a writer, photographer and artist who is active in the Great Peninsula Conservancy. She writes about the natural wonders of Kitsap County monthly for Kitsap Weekly.