#mummichog

You get a Mummichog

Today's WBW topic is a brave little swimmer that has boldly gone where no fish has gone before. Yes this tiny champion is the first fish to go to space. But you don't need to look to the skies to find these fish fascinating, there's plenty to appreciate even on Earth.

(Image: a mummichog next to someone's fingers for scale. It is about the size of a finger/ It is a small, green fish with a long body, founded fins, and silver specks that form vertical bars toward the rear of the body. End ID)

Mummichogs (Fundulus heteroclitus) are killifish that typically reach 7.5 to 9 cm (3 to 3.5 cm) but can grow up to a whopping 15 cm (6 in). There are two subspecies: the northern and southern mummichogs. The difference between them is very subtle and mostly appears in their eggs, which I'll cover in the reproduction section. Unlike most fish, mummichogs do not have lateral lines. The lateral line is a series of sensory pores that run down the body of most fish and some amphibians. The pores detect changes in water pressure, allowing the fish to sense the movement of water around them. While mummichogs have lost the ancestral lateral line, they still have sensory pores on the face. Mummichogs have a limited ability to change color, which they used for camouflage and possibly communication. Usually, they are olive green to brown, with lighter undersides. Sometimes they will display thin, silvery, vertical bars on the sides. Males change color during mating season, described in the reproduction section. Males also have larger dorsal and anal fins than females.

(Image: a male (top) and female (bottom) mummichog. The male has a shorter, more robust body with a more blunt head. End ID)

While most killifish are freshwater species, mummichogs are oceanic. They dwell in coastal areas of the North American Atlantic coast from northern Florida to Canada. Habitats include intertidal zones, estuaries, salt marshes, and up rivers. Mummichogs can tolerate a very wide range of salinity, from freshwater to almost three times the salinity of regular ocean water. This allows them to swim up rivers, though they usually stay below the head of tide (the point where a river is affected by the tides) and there are a few lake-bound introduced populations. They prefer muddy bottoms with seagrass or plants to provide shelter, but can tolerate other conditions. Mummichogs are shoaling fish that live in shoals up to a few hundred strong. Shoals differ from schools require all the fish involved to be moving together whereas shoals are any group of fish that stick together for social reasons. The shoaling behavior actually helped inspire their name. Mummichog comes from a Narraganset word that means "moves in crowds". Shoaling helps the group find food and avoid predators. A lone mummichog is more likely to be targeted by a predator than one of dozens in a shoal. Shoals also mean more eyes looking out for danger. Mummichogs are opportunistic omnivores that eat algae, small invertebrates, seagrass, fish eggs (including those of their own species), and plankton. During winter, those living on the northern part of their range will bury themselves in mud and hibernate until spring.

(Image: a group of thee mummichogs, two of which are males in mating season coloration. They have more pronounced vertical bars and orange underbellies. End ID)

Life in the intertidal zone is one of extremes and mummichogs have adapted well to extreme conditions. As mentioned above, they can survive in a wide range of salinities. They can also survive a wide range of temperature, from 6 to 35°C (59-86°F) including relatively rapid temperature changes. They survive these temperature changes by speeding up or slowing down their metabolic functions. They can also survive low-oxygen environments and can even survive for a few hours out of water as long as they stay wet. These adaptations allow them to survive in tidepools during low tide. Tidepools are harsh environments. Once a pool is isolated from the ocean, exposure to the sun can heat up the water and increase the salinity through evaporation. Oxygen is used up by all the animals in the pool and that's in addition to the issue of warmer water holding less oxygen that cold water. Mummichogs are very well adapted to survival in these hostile environments. Their ability to survive on land for a while can help in the case that a tidepool becomes too harsh even for them. A mummichog lying on its side can contract its muscles to jump many times its body length. This could help one find a more suitable tidepool or make its way back to the ocean. Mummichogs are also highly resistant to many types of environmental toxins. They can quickly develop resistance to introduced pollutants by apparently modifying their genes. One study found that a population living in a bay polluted with polychlorinated biphenyls and another living in a river polluted by creosote had about 20% of their genes modified when compared to populations living in clean water.

(Image: a mummichog held in someone's hand. This one is very dark with prominent silver bars and a white belly. End ID)

Mummichogs reproduce from spring to fall during high tide. They prefer to spawn during spring tides: especially high tides following new or full moons. They prefer to mate at night, but will in the day if necessary. During mating season, males will become more brightly colored, gaining blueish sides, silvery vertical bars along the sides, and orange bellies. These colors apparently attract mates. Females will signal they are ready to mate by turning on their sides and flicking their tails. Males will pursue females and a pair may swim together for a while before mating. When the time comes, the male will maneuver the female against a rock or plant and grab onto her using his dorsal and anal fins. They then release sperm and eggs together. The eggs of the northern subspecies have sticky filaments on them while the southern subspecies' eggs don't. They will target sheltered places at very high tide to lay their eggs, such as plants, seaweed, rocks, and shells, and the northern subspecies will also lay right onto sand or mud. The eggs will be exposed to the air once the tide goes down and will continue to develop as long as the air is wet enough to keep them from drying out. When the water returns during next month's spring tide, the eggs will hatch. The juveniles spend their first few weeks in the intertidal zone before growing large enough to move to deeper water and join shoals. They become sexually mature around age 2 and can live up to 4 years. Mummichogs can hybridize with the closely related banded killifish Fundulus diaphanus.

(Video: a female mummichog spawning. There are multiple mummichogs swimming in shallow water over a shandy bottom. A female is displaying over a bivalve shell. She repeatedly turns her body sideways over the shell and wriggles. Eventually, a male comes to mate with her. The act of mating is extremely brief and easy to miss, but both fish leave the shell afterwards. End ID)

Mummichogs are classified as least concern by the IUCN, meaning they are not at risk of extinction. They are abundant withing their habitats and capable of living in some of the most heavily polluted streams in their territory. There are rives out there so polluted that mummichogs are the only fish species that live in them. Mummichogs have been introduced to lakes, streams, and drainage ditches outside of their native range to help control mosquito populations. Mummichogs are highly effective predators of mosquito larvae. Aside from a small live bait market, there isn't a commercial interest in mummichogs. Mummichogs are heavily used in science as model organisms for stress and poison resistance due to their small size, tolerance for bad conditions, and ability to thrive in captivity. Their eggs are translucent enough to allow for microscope viewing of the process of development through the larval stage, making them useful for developmental studies. The embryos are also durable enough to be manipulated by lab equipment and survive. Their usefulness in labs contributed to mummichogs being the first fish in space. In 1973, a group of mummichogs and eggs were take aboard the Skylab space station and observed. The adults took several days to adjust to swimming in microgravity, they initially pitched forward too much and swam in circles, but they eventually figured out how to swim normally. Hatchlings on the space station were able to swim normally from birth. Since then, mummichogs have been taken on a few more space missions.

Mummichog!

Killifish!

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.

And the result?

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.