Gill lice detected for first time in Virginia trout

‘Not a statewide emergency,’ wildlife officials say

By: - April 19, 2022 12:02 am

A rainbow trout. Wildlife officials have found a species of gill lice for the first time in Virginia. (Jason Hallacher/ Virginia Department of Wildlife Resources)

Native brook trout in Virginia appear to be out of harm’s way when it comes to the recent detection of a nasty aquatic parasite called gill lice in Southwest Virginia. 

Biologists from the Virginia Department of Wildlife Resources sent samples of gill lice found on rainbow trout in Blue Springs Creek in Smyth and Wythe Counties to a laboratory to verify which species had been detected. 

The U.S. Fish and Wildlife Service Lamar Fish Health Center confirmed the samples to be Salmincola californiensis, a species that is host specific to rainbow trout, the DWR announced last month.

Another species of gill lice, Salmincola edwardsii, is host specific to brook trout but has not been detected in Virginia. 

“The two species of gill lice are very specific to the host species, in other words the one that generally infects rainbow trout would not likely infect brook trout and vice versa,” said Jeffrey Williams, DWR regional aquatics manager. 

Both species of gill lice are already present in North Carolina and Pennsylvania waters. 

“As we’re dealing with the species that infects rainbow trout, we are still going to be extremely vigilant looking at our brook trout populations to make sure we don’t see any appearance of the gill lice that affects brook trout,” said Williams. 

DWR biologists are not sure exactly how the gill lice made their way into Virginia, but they will assess private hatcheries in the Cripple Creek watershed since no gill lice were detected in state hatcheries. 

Gill lice in the mouth of a fish. (Virginia Department of Wildlife Resources)

“The fact it’s here now is generally thought to have coincided with stocking of rainbow trout to other parts of the U.S. east of their native range,” said Williams. “This has been a long term transition. We just had not seen it here in Virginia until this point.”

Rainbow trout are native to the Pacific Northwest but have been stocked throughout the east coast since the late 1800s. 

“Certainly the private operators in the state do everything they can to keep their fish happy and healthy and to be good stewards of the environment,” said Brendan Delbos, state hatchery superintendent. “We are not throwing private industry under the bus or blaming them. This is just a new pathogen that’s popped up, and we’re working together to figure out the best way to deal with it.”

A light gill lice infection is usually not detrimental to a rainbow trout’s overall health, but a more serious infection can affect a fish’s ability to breath, eat and ultimately survive.  

Gill lice can have other physiological impacts on trout such as inhibiting proper growth and movement,” said Alex McCrickard, DWR aquatic education coordinator. “All of this can weaken a fish’s immune system, making them more susceptible to other environmental stressors such as warm water and lower concentrations of dissolved oxygen.”

Fisheries managers are now focused on limiting the transfer of fish from an infected waterbody to one that does not yet contain gill lice. They are asking anglers to clean their gear with fresh water and allow it to dry in the sun between moving from one waterbody to another as a safeguard against involuntary spread. 

“As of now it looks to be somewhat isolated, and that would be a best-case scenario if there is one in this instance,” said Williams. 

There is no way to remove gill lice from an infected population in the wild, but the fish are completely safe to eat as long as they are properly cooked. “It may be unsightly, but it’s an external parasite, and it is not found inside the flesh,” said Williams. 

Virginia is part of a growing list of regions outside the Pacific Northwest that now have gill lice, including the Great Lakes, Pennsylvania, North Carolina and Colorado. 

“I do think it’s fair to say that this is not a statewide emergency,” said Delbos. “Certainly it’s a novel pathogen for us here in the state. We are concerned about it and we’re keeping an eye on it, but this is not going to wipe out the fisheries or the rainbow trout population in the state.” 

Officials are asking trout anglers to help monitor for any further spread by reporting gill lice sightings to [email protected]

“All it takes is an extra second to look in the gills and down the mouth. If you see anything, please report it,” said Williams.

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Evan Visconti
Evan Visconti

Evan is a freelance journalist and photographer, covering environmental news. Originally from Tully, New York, he graduated from Loyola University Maryland in 2019 and then earned his master's degree in journalism from Emerson College in 2020. He has reported on stories including offshore wind energy, dairy farming, and tribal land conservation. Contact him at [email protected].