Signal-box painter in Jamaica Plain highlights threatened species, including one found only in a small pond near the Muddy River

Jovielle Gers's mural on a traffic-signal box at 3201 Washington St. in Jamaica Plain has depictions of four rare species in Massachusetts: A piping plover, a red-bellied cooter turtle, gerardia flowering plants and a tiny fish, known as the threespine stickleback, which has its only Massachusetts freshwater population in a small pond that feeds into the Muddy River in Jamaica Plain.

Threespine sticklebacks as a whole are not threatened - they're found across colder waters in the northern hemisphere - but most live in salt water, then migrate to fresh-water streams to spawn. In contrast, the Jamaica Plain sticklebacks just stay where they are in their Emerald Necklace hideaway - a pond so small it has no name, off Willow Pond Road and the Jamaicaway, behind where the skating rink used to be. This tiny pond is the only place in Massachusetts where you can find exclusively freshwater threespine sticklebacks and the southernmost place on the East Coast to find that version of the fish, which grow to maybe 1 1/2 inches.

Also, unlike other threespine sticklebacks, which have one of three types of rear-body armor - either completely going back to their tail, halfway, or barely any at all - the JP ones come in all three forms. Some even have four or five spines instead of the usual three. Like other male sticklebacks, after fertilizing eggs from females in an underwater "nest," the males guard their brood, fanning them to ensure they get enough oxygen, until they hatch and mature.

A 1984 report included a description of a 1979 sampling project up and down the Muddy River basin, such as it is, to find other examples of the fish, but none were found outside that one unnamed pond. The report also describes how, in 1981, researchers used a net to catch 230 of the fish from the pond, then dumped them, live, into a formaldehyde solution, to study them.

Nobody knows how the fish wound up there. Although the Muddy River flows into the Charles, which was once a tidal estuary, it's essentially been cut off from ocean waters since Olmstead directed construction of Charlesgate to try to reduce the stench of exposed sewage in the Fenway section of his Emerald Necklace in the 1880s. The Charles itself was turned into what is essentially a freshwater lake by the construction of dams after the turn of the century for much the same reason, although the current dam does have a fish ladder for the hardier anadromous fish.

The box that Gers painted on Washington Street is a little less than a 1.5-mile walk from the pond.

Gers said she hopes the mural will “raise awareness and inspire awe at the beauty of these incredible creatures and bring them in a safe way right into the middle of the city. I believe the more we can experience awe on this incredible planet and awe at our chance to be alive, the more respect we will have for the mystery and beauty of life.”

H/t Greg Cook.