A small fish native to China has been found swimming in the San Joaquin River, and scientists warn that it could join a list of exotic, invasive species that have colonized California.
The fish belongs to the loach family. It was discovered in October by wildlife scientists doing restoration work on the San Joaquin River in Madera County. Returning a month later, the scientists found six more loaches of the same type, said Ron Smith, program manager of aquatic invasive species at the U.S. Fish and Wildlife Service.
Although it could take another two months or so to determine the exact species, Smith said scientists are certain the fish did not previously live in any river in California or North America. DNA tests conducted at UC Davis’ Genomic Variation Laboratory narrowed the species down to two variants of a fish called the Chinese fine scale loach.
“The Chinese loach is native to the Yangtze River and other nearby rivers, so (it) lives in conditions similar to those in the San Joaquin River, at least in summer and drought winters,” said Peter Moyle, professor at the Center for Watershed Sciences UC Davis.
In the U.S., the Chinese fine scale loach is used in ornamental aquariums. Often the fish is sold, unwittingly, as other loach fish species.
The fish grows from 6 to 11 inches and is most commonly found in Asia amid shallow, slow-moving sections of rivers and streams and in calm habitats such as swamps.
The loach is also used as a bait fish in Asia. It is illegal to use the Chinese fine scale loach as bait in California.
The most likely culprit for the fish’s appearance in the San Joaquin River is aquarium dumping, said David Catania, fish librarian at the California Academy of Sciences.
The U.S. Department of Fish and Wildlife recently sent samples of the fish to Catania to corroborate the UC Davis findings. The academy houses one of the largest and important research collections of its kind. In 2014, it provided the identification of 24 new species of fish. Catania said it could take about two months to identify the newly discovered loach.
Catania said he believes the loach likely came from an aquarium. That was the case with the lionfish, a species from Asia that is now well established on the East Coast and in the Caribbean.
An extremely popular ornamental aquarium fish, the lionfish quickly outcompeted native fishes and has been affecting snapper and grouper populations.
“This loach is not native,” Catania said. “Whatever the fish is, it’s invasive.”
The closest relative to the Chinese fine scale loach found in California is the oriental weatherfish loach – also an invasive species now thriving in Southern California, and also found in 13 states.
“The loach species is very adaptable. They do well in a very wide range of environmental conditions,” Smith said. He said changes in habitat caused by drought can benefit adaptable invasive species at the expense of environmentally sensitive native species.
Drought conditions have altered the San Joaquin River. Water levels are so low that the loaches were found in isolated pools, Smith said, adding that if the river’s flow had been normal the six fish found in November would likely have gone unnoticed.
The Chinese fine scale loach may also share a trait found in other loaches – which have been known to survive for extended periods outside of water in mud and sand environments, Smith said.
Smith said that until the species is fully identified, it will be difficult to predict its invasive potential. “Invasive fish species are notoriously difficult to control once established, “ he said.
In a large water system like the San Joaquin, it could be especially difficult to eradicate the newcomer. “Control methods are relatively catastrophic,” Smith said. “It can cause damage to what is there and sometimes damage to other species.”
Smith cited the eradication of the northern pike in Lake Davis as an example.
Northern pike, native to an area from Nebraska to New England, was first identified by an angler at Lake Davis in 1994.
It quickly became invasive and threatened the lake’s trout population. At the time, the fear was the pike would wreak havoc on native fish species downstream in the Feather and Sacramento rivers, and possibly the Sacramento-San Joaquin Delta.
Eradication efforts by the California Department of Fish and Game proved controversial, and costly. In 1997 the organic insecticide Rotenone was dumped in the water to kill the pike, but it also poisoned most of the fish in the lake.
The northern pike returned. A second, more thorough eradication, in 2007, led to removal of the pike and eventual restocking and recovery of the native fish in Lake Davis.
The cost of eradication: $20 million.
Call The Bee’s Edward Ortiz, (916) 321-1071. Follow him on Twitter @edwardortiz.