Marine Biology Story of the Day #10
Hello all. This post was kinda delayed because I spent all day cleaning out my pool (it’s an above ground pool—my COVID 19 impulse purchase) because a hurricane came through and it’s full of dead insects and leaves among other things. The joys of living right on the coast 😊
Thanks for all of your interest and support on my shrimp research—it’s nice to know that people are interested in the little guys too. So today, we are going to talk about how all of my interest in tiny fish got started—my master’s program and my thesis.
SOoooo…originally I wasn’t planning on getting my masters because it sounded like a lot of work but then I changed my mind last minute when I started looking at job applications and saw that for many of them, you needed a masters—so I ended up becoming a master’s student at the same University that I did my undergrad at—called Christopher Newport University. It’s a teeny public school in Virginia near the Chesapeake Bay. And the reason I chose to do this is because I would be working under Dr. Jessica Thompson, who in hindsight, was probably the best advisor I could have had.
Dr. Thompson is a wonderful human being with many beautiful tattoos, and can definitely drink me under the table, and raises chickens in the middle of a city, but she is also pure and wholly supportive—something that I really needed during that period of my life. She also exclusively studied a wonderful teeny tiny fish: Fundulus heteroclitus, or the Mummichog.
(The males are the ones with the stripes and bright shiny scales and the female is the drabber one)
Her research focuses on this little fish because it is one of the hardiest fish on the east coast. It primarily lives in shallow water salt marsh habitats (intertidal marshes). These shallow water habitats often have very extreme temperature and salinity changes, as shallow water heats and cools up much faster than deep water. So they can survive in a wide range of temperatures, salinities, and dissolved oxygen conditions—I call them the cockroaches of the sea (except they are much cuter). They are also a very important food resources for a TON of marine and coastal predators.
They were also the first fish in space—and they were used in spatial orientation studies. You see, in space, animals and plants can lose all sense of up and down because there is no gravity—however in a few days, this fish were able to figure out their spatial orientation (possibly due to orienting to the overhead light source?). Anyway, they are incredible little babies.
(NASA scientist John Boyd choosing the first two fish (and fish eggs) to leave planet earth)
Because they can move into the very shallow intertidal marsh area (the part where the grasses grow) they can avoid predators during high tide, and this area of the marsh is chock full of food for them, mostly in the form of small zooplankton and worms that live in the mud. But during low tide, this part of the habitat dries up, and they are forced out into the deeper subtidal creeks of the marsh, where they get to be in cooler water, but they are at the mercy of predators, and there is less food.
(everything in the open water is subtidal, everything between tidal flat and low marsh is intertidal)
My aspect of this research involved looking at behavior choices made by these guys when presented with “intertidal marsh” habitat filled with food and marsh grass (their preferred habitat), however we cranked the temperature up to 34-40 oC (93—104 oF), OR a empty “subtidal creek” habitat with no food or structure, but at their optimum temperature for growth at 26 oC (79 oF). 34-40 oC is an EXTREMELY high temperature for fish to be able to function at—most fish begin shutting down their metabolism at these temperatures (aka dying). But supposedly, Mummichog can deal with these temps. There thermal maxima (upper temperature at which they can function) is reported to be 42 oC.
So I had to construct an experimental tank.
These were some of the first iterations of the tank—we had to do a lot of practice runs before we got the design just right. The concept is the same—we used this corrugated plastic (the same you use to make those political signs ppl stick in their front yard) to form two sections, one for warm, one for cold, and a box in the middle that we would remove a door and allow for the fish to swim out. Once the fish chose a side (remained on a side for more than 10 seconds) we would close them off from the rest of the tank—they made a “choice”. In later iterations of the design, we covered the tank in more of the plastic to hide them from us (so they wouldn’t show fear behaviors) and put in fake salt marsh grass on the warm side to mimic an intertidal marsh habitat. Fish were also fed pieces of cut up shrimp on the warm side. We ran 3 trials at increasing temperatures for each run, and during each trial, the fish were run through the tank simulation once a day for three weeks.
In order to get fish for this study, we had to catch wild fish. To catch them, we set minnow traps in the small channels leading into the intertidal marsh at low tide, and as the tide came in, and fish funneled into these channels, they became trapped in our minnow traps.
(examples of minnow traps, and our collection site in Norfolk)
Problem was, in order to get out to these sites, we had to slog through some serious mud. I’m talking about sink up to your thigh levels of mud y’all (and this really bothered me, I’m super claustrophobic). So in order not to get trapped in the mud, we had to wear mudders, which are a little bit like snowshoes (in concept?) but also not like snowshoes at all. They were like boxes you strapped onto your feet with plastic sticking out on the side which was meant to make your footprint bigger (and therefore give you more support on the mud). They worked pretty well but they always gave me major bruises on my ankles as the plastic pressed up and into my ankles. I had to buy some foam padding to wrap around my ankles it was so bad.
Once we got our sweet little babies, I would tag each of them individualy so I could keep track of individual fish. I did this with a combination of Visible Implant Alpha Tags, which are florescent and have individual numbers on them, or Visible Implant Elastomer Tag, which are made of a non-toxic elastomer “paint” and come in 9 colors, so you can create an individual code for each individual by combining 2 colors. These tags are injected under the skin so that they are still visible (fish skin is pretty transparent) but are not very deep in the muscle tissue. These are really great tags to use on really small fish. We used MS-Tricane to anesthetize the fish and inject them, so basically I’ve done fish surgery. You can check out these tags at Northwest Marine Technology—I still use them now! I’m using them on a current project.
(left, a VI Alpha Tag on a trout, right, two different colors of VI elastomer tags on a flounder)
And our fish did really well after tagging—we had no tagging mortalities!
Once we ran these fish through all three trials, it was time to analyze data. We calculated the fish’s dominant “choice” by calculating the proportion of days during the trial they chose the “warm side”—if their proportion was 90%, they had a high affinity for choosing the warm side, 30% they had a low affinity for choosing the warm side and instead more often chose the cool side for example. Then we put this data into environmental models to see if temperature influenced their choices.
You read it here first folks. These little fish decided to swim into upwards of 104 o C water regularly to get food—they were so food motivated—and most fish chose the warm side over the cool side most often during every trial. However there was a decent amount of variation—there was a contingent of fish that went into the cool side more often as temperature rose, and would forgo eating for comfort, but overall, the fish chose the warm side. This shows that these fish may be able to adapt quickly as temperatures rise—and those that choose to move into warmer, shallower waters to access food will more likely survive to reproduce (since they choose to be in regions with less predators and more food). This means they are more likely to pass on their warm water acclimating genes to their offspring, continuing their species ability to deal with extreme temperatures on to the next generations.
My thesis defense obviously went well, and I got my masters, but I’ve kept my interest for the smaller fish and invertebrate species because they form one of the base levels of our ocean ecosystems and serve as a very important food resource to larger predators. I’d like to credit Dr. Thompson for giving me this interested and giving me the appreciation for these little and underappreciated animals. She and I have kept in touch—she was actually at my wedding last May, and when my dad got in a major accident (four days before I was supposed to defend my thesis) she came to the hospital and helped me through it, and also helped me push back my defense one semester so I could recuperate from the trauma a little. I am extremely grateful for her tutelage, and I’m grateful for these sweet little babies.
Thanks for reading, and as always, if you have any questions about the field work or the research, PLEASE do not hesitate to ask or comment.
