Category: Genetics

Fish Phlebotomy 101

7/24/2016

Blood is drawn from the caudal vein just behind the anal fin. How do you learn to do this? You watch a lot of YouTube videos.

he name of the game is the same: It’s hot, dry, and the fish are disappearing from predation. On Monday there was a panic when we showed up to track and there were several new tags gone. From here, the short-term plans I was brewing for the study went up in a gigantic ball of fire, and the lighter fuel looked something like this:

11:30am: A thunderstorm rolls through the area. I find spotty cell service to check the radar and I email my advisor a quick update (mostly to occupy my boredom). After an hour the storm clears, I’ve heard nothing from my advisor, so I carry on with my day none the wiser.

8:00 pm: I get back to the house after tracking and check email before going to bed. I find it odd that my email is taking a while to load, until I realize there are 67 new messages. I scroll down and see the names of my advisor and other collaborators popping up a few more times than they should. This can’t be good.

9:00 pm: After talking to my advisor, we decide to start sampling ASAP. This is why you don’t check email before bed.

1:00 am: Sampling crew contacted, weekend trip to Virginia pushed back, sampling supplies inventoried, mini panic attack that I just moved up a major aspect of my project by over a month.

Only four tiny gill filaments are needed for our analysis. Fish gills get damaged frequently, so they don't even notice the missing filaments after they are released.

An added benefit to sampling now is seeing what fish await for fall tagging. I'm hoping I can find this fish again in a few weeks.

So, why the sudden change? I’ve mentioned before that we take a gill and blood sample from every fish that we tag. One of the reasons we do this so that we can determine how fish are responding to temperature stress at a molecular level. In the spring we collected tissue from fish that were loving life at stream temperatures near 50°F. This is the equivalent to a relaxing spa day for us, and so it serves as a baseline for what tissues look like when fish are not stressed.

Fast forward and now trout are trapped in water that is 15° warmer and some of the molecular markers have changed in response to the heat stress. But, just like when you come inside to air conditioning after a hot day in the sun, as soon as the water cools down fish will return to baseline. Not knowing how long we have before the heat streak snaps, and because we have already lost so many tagged fish, we had to pull the trigger and push the sampling up.

We are still trying to decide exactly what we will look for in the tissue samples, but one focus right now is heat shock proteins, or HSPs. HSPs are produced by cells in response to heat stress to prevent cell death and are easily detected in the gills of fish. We know we should find a difference in HSPs from spring to summer to fall, but that’s not all that exciting (it will basically just tell us that HSPs are more prevalent when it’s hot).

But, more interestingly, we are curious whether some populations show an adaptation to chronic heat stress. While HSPs are necessary to prevent cell death, they are produced at the cost of reduced growth and reproduction. So, fish can’t just produce a bunch of HSPs because then they won’t have any energy to survive. We are curious whether populations that are exposed to more heat are more efficient producers of HSPs, are acclimated to heat and don’t produce as many HSPs, or if heat is stress that can’t be overcome.

We lucked out and accidently picked one site that is not only warmer than the others, but also more variable in temperature. So, we are curious to see how HSP production differs in that stream in comparison to the others. Regardless of the result, this is one of the first studies of HSPs in natural trout populations, so the results will help us forecast trout response to future warming or at least design follow-up studies to address the question.

For now, we have sampled a little less than half of the study sites. When we sample we are only targeting fish that are currently tagged, so in theory it should be easy. Wrong. These fish are incredible at finding little crevices to hide in, and despite knowing a tag is within 5 feet of you we are still averaging about 30 minutes or more per tag. The dilemma is deciding when to keep trying to recover the tag because you think it’s a hiding fish vs. when to give up because it’s a dropped tag in a deep hole. So, we’ve been throwing rocks, wanding heavy magnets to pick up tags, and pumping voltage (special thanks to Steve and Linda Szoke, who volunteered the first day and taught me a little patience in this task!). Slowly but surely, we’ll get there.

Loyalsock sampling resumes next week, but for now I’m in Virginia for a few days to catch up on non-field life and to help sample an urban stream I’ve been working on since 2006. Why do I volunteer to sample a tiny stream in July when it’s at least 100°F and the bulk of the work is counting juvenile minnows? You’ll have to stay hooked to find out….