JALISCO, Mexico » Last week, while sailing the Honu out the Barra de Navidad channel, I spotted a white round float.

"Which side of this buoy do you think I should take?" I asked Craig.

"That’s not a buoy," he said, peering ahead. "It’s a navigational pufferfish."

It was a good name for those living beach balls floating on the water’s surface. They have tricked us here time and again.

Fish that can blow themselves up with water, or air when they’re at the surface, are grouped into two families: pufferfish and porcupinefish. Since they all puff up as a means of avoiding being bitten or swallowed, I’ll just call them smooth and spiny puffers.

It’s the spiny puffers, also called balloonfish, here that have surprised us. Besides sometimes viewing them as steering markers or floats for crab traps, we also thought that when upside down they were dead.

Once, after determining that the white floating sphere was a large spiny puffer, I directed Craig to steer the boat close enough to collect the dead fish. My idea was to dry it and hang it in the boat as a tribute to the remarkable puffers.

As soon as I scooped the fish sphere into a bucket and hauled it aboard, it began to sputter. As I lowered the bucket back to the surface, the fish continued to spit and snort. When it hit the water, it was gone.

Usually, but not always, puffing up works as a defense. In 1958 a researcher off the Pacific coast of Colombia spotted a sea snake floating next to an inflated porcupinefish. The snake was trying to bite the fish but couldn’t get hold of it. On the other hand, sharks have been found dead with inflated pufferfish, also dead, stuck in their throats.

The other pufferfish that tricked me was a smooth one, called the guineafowl puffer, a striking foot-long fish with a navy blue body covered in white spots. Found throughout the Indian and Pacific oceans, including Hawaii, the abundant guineafowl puffers I found here were unafraid, curious and often approached. Another pufferfish, the same size as the guineafowl but a brilliant yellow, also swam up to me.

I later looked up these two fish in my books and discovered they are the same species. The yellow one, considered rare, is a golden phase of the blue one.

One book had a photo of a blue one in the process of turning yellow, its dark body mottled with light spots. Why a blue-and-white individual changes color, no one knows.

I’m just glad they don’t have aspirations to become navigational pufferfish. Yellow buoys signal danger.

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Reach Susan Scott at www.susanscott.net.