Bluefin killifish. Photo courtesy of Phil Voong.
Yet another non-native aquatic species may have made itself at home in the Delta.
As described by US Fish and Wildlife Service fish biologist Brian Mahardja and his co-authors in San Francisco Estuary & Watershed Science
, the newcomer is an inch-long, minnow-like fish called the bluefin killifish
(Lucania goodei), indigenous to Florida and adjacent southeastern states. It was first detected in the Delta Cross Channel during a beach seine survey in October 2017, and subsequently found in Beaver and Hog sloughs and at Decker, Sherman, and Brannan islands. With surveys curtailed by the coronavirus pandemic, current data is sparse, although 13 were caught before March and one was caught in June. Bluefin killifish are popular in the freshwater aquarium trade, and the authors suspect the founders of the Delta population were released by a former owner near the Sacramento River, which connects with the Delta Cross Channel in summer and fall. “It’s highly likely that the species is established in the Delta,” says Mahardja. Its life history suggests strong potential: it requires fresh water and submerged aquatic vegetation, has survived temperatures as low as 8.9 degrees C (48 degrees F), and is a fecund spawner with a long reproductive season. Climate change may improve the killifish’s overwinter survival, and planned tidal wetland restoration in the Delta will expand its preferred shallow water habitat. It’s not clear how the killifish interacts with other species and there’s no funding to investigate; Mahardja says the beds of exotic vegetation where it feeds and breeds aren’t heavily used by native fish. Still, even a small fish in the wrong place can cause big problems. This one highlights the underappreciated role of the aquarium trade as a pathway for introductions. Co-author and FWS colleague Louanne McMartin says a “Don’t Let it Loose”
program (similar to the “Don’t Plant a Pest” initiative for horticulturists) has been created to educate retailers and fish fanciers about the risks: “It is important to engage the public to bring about a change of behaviour, such as preventing people from dumping fish bait and releasing pets into our waterways that could result in the introduction of an unwanted species.”