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.”
Pearls in the ocean of information that our reporters didn’t want you to miss
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.”

About the author

Joe Eaton writes about endangered and invasive species, climate and ecosystem science, environmental history, and water issues for ESTUARY. He is also "a semi-obsessive birder" whose pursuit of rarities has taken him to many of California's shores, wetlands, and sewage plants.

Related Posts

August 31, 2022

Climate change is heating, salinizing, and expanding the San Francisco Estuary, a review of nearly 200 scientific studies concludes.

Sea level rise, changing snow and rainfall patterns, and warmer waters are some of the changes already observed in the Estuary and expected to continue through the rest of the century as greenhouse gas concentrations rise. Changes to water are at the heart of the documented and further expected impacts;...
August 31, 2022

Groundwater pumped from subsided islands back into Delta channels through 200 or more active outfalls can be laden with excess nitrogen transported from island soils, report the authors of a new study.

The Sacramento-San Joaquin Delta contains more than 50 peat islands. Most have subsided—some as much as three meters — as a result of drainage for farming, and must maintain artificial water tables below the land surface via managed pumping. According to researchers from the University of California at Santa Cruz...
December 15, 2021

A large pulse of water sent through the Yolo Bypass in summer 2016 boosted phytoplankton biomass and food web conditions in Cache Slough and the lower Sacramento River, a new report confirms.

 “Our goal was to improve estuarine habitat by increasing net flows through the Cache Slough Complex to enhance downstream transport of lower trophic-level resources, an important driver for fish such as the endangered Delta Smelt,” write the authors—including esteemed (and recently retired) California Department of Water Resources lead scientist Ted...