On April 18, the day after a rainstorm flooded parts of Oahu, several readers emailed that hundreds of dead fish lay on Kailua Beach, and wondered what they were. It was late morning before I could get to Kailua Beach Park, but after walking its length, I saw no dead fish. I then went to Kalama Beach Park but found no fish there, either.

Back at the boat ramp, a man told me, “The tide took them. They were catfish from the canal.” But when a friend later emailed me a photo of one of the dead fish, it didn’t look like a catfish to me.

The canal the man referred to is the Kawainui Canal, also known as the Kawainui stream. Some know it as the Oneawa canal because it flows under the street by the same name, the main thoroughfare of Kailua.

The stream lies on the north end of Kailua Beach Park and collects water from a spider web of waterways connected to Kawainui Marsh, a Kailua jewel. During my last stroll there, I found Hawaiian coots, stilts, gallinules and ducks. I had no idea, however, what kind of fish lived there or in the canal that drains the area during floods.

A book I have called “Hawaii’s Native and Exotic Freshwater Animals” (Mutual Publishing), by Mike Yamamoto and Annette Tagawa, enlightened me on this subject, which I know little about.

According to the biologist authors, Hawaii’s freshwater streams and canals host at least six kinds of catfish and several other non-native fish species. The Chinese catfish, or puntat, came with Asian immigrants in the 1800s. The channel catfish was introduced from the U.S. mainland. Others came from South America and various Asian countries.

The scientific name for catfish is Siluriformes, a group of about 3,000 species found on all continents except Antarctica. Because catfish are hardy and good to eat, countless species have been imported to ponds and streams around the world, including Hawaii.

The name “cat” for these fish refers to the whiskers on the fish’s face. Like our marine goatfish, the whiskers, called barbels, are the fishes’ taste organs. They look nasty but do not sting.

Another introduced fish in our streams is the chevron snakehead, or pongee, also brought from Asia in the 1800s. Several stranded fish in the photo my friend sent looked like the book’s pictures of pongee.

Or not. Biologists are discovering more and more alien species in our streams because people release unwanted aquarium pets into Hawaii’s waterways.

When this spring’s heavy rain caused the Kawainui Canal to flood, the muddy water overpowered and/or suffocated some of the fish living there, washing them into the surf, which heaved them onto the beach. As a result, Kailua’s early beach walkers got a rare view of Oahu’s introduced freshwater fish.

I missed seeing them, but friends who did tell me to count my blessings. I missed smelling them, too.

Reach Susan Scott at susanscott.net.