Lice Lice, Baby

March sampling with a stream temperature maxing out at 32.2F. This day sucked.

There’s no way around it. Sometimes my job sucks.  Like days when I’m sampling in sub-freezing temperatures in November, or grabbing my gear as I hear the weather man use words like “oppressive heat warning.” There’s also 18-hour days, days spent hiking up cliffs, days where you feel like you must be wallowing in a pit of stinging nettle, poison ivy, and mosquitos, and days were all three of those events combine.
 
And then there are days where I have the burden of electrofishing a stream loaded with 9+ inch native brook trout in the breeze of an unseasonably cool summer day.
 
Yeah, I didn’t say my job always sucks. And, this week, my job didn’t suck.  In one of the easiest field days in recent memory, we recruited 22 new brook trout into my study (yes, I know I just jinxed myself, but I’m hoping it’s retribution for some of the other days I’ve had this year). That’s 22 more blood and gill samples packed away in very deep freeze to be studied for their expression of stress proteins.
 
In most of my field work descriptions, I’ve taken the easy way out and said I’m collecting a “blood sample.” That’s not entirely accurate. I’m collecting a blood sample, which I then use to get a plasma sample. Though it is the largest component of blood (making up about 55% of blood, by volume), plasma may seem a bit foreign to you unless you’ve donated or received it. Masked by the more obvious color of red blood cells, straw-colored plasma is practically invisible when suspended in whole blood. But, it’s made up of some of the most important elements in the body- water, salt, enzymes, and, you guessed it, proteins. This includes all the stress proteins we are interested in measuring as stream temperature rises.  

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The Loyalsock Fish Plasmapheresis Center. It was significantly remodeled now that we use an electrical outlet rather than the truck battery on the side of the road.

With a little know-how, it’s actually quite easy to separate red blood from plasma. The folks at the American Red Cross do it with a big machine that takes your whole blood and spins it in a circle really fast (otherwise known as centrifuging). Red blood cells are heavier than plasma, so centrifuging pulls the heavier red blood cells to the bottom, and the lighter plasma components to the top.  Once separated, it’s then possible to remove plasma and, in the case of the Red Cross, return red blood cell components back to the donor.
 
In the fish world, we do things a bit differently.  First, there are no big machines.  There are small centrifuges running off car batteries or borrowed electricity from the Snack Shop at World’s End State Park (the view is inarguably better here than in the plasmapheresis center). And, forget return to donor, we’re greedy and keep both the plasma and red blood for analysis.  But, other than that, the process is about the same.  Collect blood, centrifuge blood, remove plasma, repeat. (We may also be feeding ourselves the sugary post-donation snacks. But, we checked, the fish don’t mind.)
 
In total, it takes about three hours to remove plasma from 22 blood samples. And, what would you know, we meet a lot of people curious as to why there’s a few college kids with a centrifuge and sterile gloves next to the Snack Shop. Luckily, I like to chat fish to anyone willing to listen. And, I’ve pretty much memorized my spiel when asked “what the heck are you doing?” So, I start chatting about climate change, fish movement, and gene expression.  And, you want to guess the number one question I get asked in return?

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Have you found any gill lice?
 
Seriously?  I’m over here teaching a course in fish phlebotomy and toting around the equipment that allows me to electrocute fish WHILE I walk in the water, and you want to know about a parasite?  Move along!
 
In all seriousness, I do get asked some great questions about my research, and I appreciate that so many people are so attune to this rising threat. Fortunately for me, even after taking gill biopsies from over 400 fish in the last year, I have never personally encountered a trout infected with gill lice. And, I am thankful for that.
 
What’s the big deal with gill lice?  Despite the name, gill lice are not related to the form of head lice common to elementary schools and daycares. Gill lice are small crustaceans (yes, just like shrimp, crabs, and crayfish) in the genus Ergasilus. Male gill lice free-float throughout the water column and females attach to the gills of fish. That may seem innocent enough, but once attached gill lice start feeding on blood pumping through gills, thereby interfering with a fish’s ability to “breath” (absorb oxygen and release carbon dioxide). After prolonged, intense infection, fish can have reduced growth and reproduction, compromised immune systems, altered behavior, and can eventually die.
 
Gill lice are a bit unique in that they are host-specific, meaning any given species of gill lice (of which there are several) is selective as to which species of fish it is willing to parasitize. So, there is a species of gill lice for brook trout, and a gill lice species for rainbow trout. So far, gill lice in Pennsylvania have only been shown to infect brook and rainbow trout, but other species of gill lice have been shown to infect salmon, bluegill, bass, walleye, and yellow perch, among many others. 

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An up-close look a few gill lice. Image courtesy of henrysfork.org.

While the press coverage is new, gill lice have been infecting streams throughout the United States for decades.  It was only recently that gill lice started making front page headlines in Pennsylvania when a large outbreak was discovered in Centre County in 2016. The origin of the gill lice in Pennsylvania can be debated, as they could have gone undetected in wild streams for years prior to the 2016 discovery.  However, there is also a smoking gun pointed towards a cooperative fish hatchery, which was known to have infected trout in the hatchery around the time of discovery. Regardless, what we know now is that gill lice have established residence in many Pennsylvania streams. And, once we started looking for gill lice we kept finding them. So, the number of streams infested with gill lice only continues to climb.
 
How many streams are infected with gill lice? We don’t know.  How are gill lice affecting trout populations in Pennsylvania?  We don’t know.  And, how can we stop the spread?  You guessed it, we don’t know.  So far, the state is trying to minimize the spread by decontaminating hatcheries and sampling streams to determine the extent of infection. It’s going to be a tough battle, though, because gill lice are resistant to chemical treatments that can be used to reduce parasite loads. So, unfortunately, managers’ hands are largely tired in trying to eradicate the parasite from wild streams.
 
While we in Pennsylvania may be on the very start of an outbreak, we can look west to predict how trout populations may fare.  Reports from Colorado and Wisconsin suggest two important things.  First, trout populations decline after gill lice infestation.  Second, warmer temperatures lead to higher infection rates. This could be because gill lice are more productive in warmer temperatures, trout become more susceptible at warmer temperatures, or a combination of both.
 
What can you do to prevent the spread?  As a general rule of thumb, always disinfect your gear when you’re leaving a stream.  This includes hopping across major watersheds, but even if you’re just moving between neighboring tributaries. Gill lice may be present without you knowing it, and even if they aren’t you can help prevent the spread of other aquatic and terrestrial invasives. Also, it goes without saying, don’t move fish between streams, as this could result in new infections.
 
When you’re fishing, keep an eye out for little rice-like nodules on the gills, opercula, or pectoral fins. Take a picture if you can, and report any suspicious findings to your local authorities. It’s always disheartening to put another stream on the infection list, but it will help managers contain the spread and devise a plan forward.
 
Also, keep in mind, stream temperatures are rising and for many it’s getting close to that time of year where you should consider switching your target species. Angling mortality greatly increases at 65F and above, so take a thermometer and fish responsibly. 

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