Koi make an easy osprey snack

When I was a kid in Robbinsdale we occasionally kept goldfish as pets in the usual small bowl. When my sister and I began ignoring them my mother flushed the fish down the toilet.

Today, some goldfish, reaching the end of their domestic welcome, are illegally released in neighborhood lakes. They thrive there, some to be eaten by ospreys.

"Natural selection doesn't favor brightly colored fish with predators like ospreys around," I was told by Jim Levitt, a fisheries biologist with the fisheries division of the Minnesota Department of Natural Resources.

The birds also will eat koi, the expensive form of goldfish. Koi are snatched from private ponds where they are kept as pets or ornaments.

In early fall this became a brief topic of e-mail conversation among a few local birders. It began when someone reported an osprey carrying a fish with a reddish hue. What could it be?

It was a goldfish or a koi.

Several times I've seen ospreys in our neighborhood carry bright golden fish to their nest. These are not the finger-size goldfish you win at the State Fair to your mother's dismay. Some of the fish these birds catch are big enough for your plate or mine.

Late fall migrants to wintering sites on our eastern and Gulf shores, osprey also eat snakes, birds, frogs, reptiles, mammals, crustaceans and other invertebrates.

Goldfish are indeterminate growers, increasing in size until they die. They are members of the carp family, reaching sexual maturity in a year. They can spawn more than a thousand eggs at a time, multiple times a week.

Koi are a subspecies of carp distinguished by color, larger size and higher price. Koi used for breeding, genetically less likely to revert to carp, sell for as much as $10,000 each. That would be an expensive osprey breakfast.

Releasing pet fish into natural waters — lake, rivers, neighborhood ponds — is against the law here. Regardless of color or price, after a few generations goldfish and koi revert to carp, natives of Eastern Europe and Asia, an invasive and unwanted species.

Levitt, the biologist, said that goldfish and koi are present in many of our lakes and ponds in the metro area.

I will not comment on my mother's disposal alternative — flushing fish fallen from favor. Mothers know best.

Vanessa Greene, who by herself is the Twin Cities Metro Osprey Watch, wrote to tell me that "most ospreys are happily eating bullheads, sunfish, crappies, perch, bass, smaller walleyes and northerns.

"After 27 years in the field I can truthfully say most of what ospreys are eating are not goldfish or koi," she said.

Greene this year monitored over 150 metro-area osprey nests. You can find more information about the birds at Ospreywatch.blogspot.com.