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The mummichog: the first fish in space

This month I wrote a guest blog for Scientific American about the first fish to leave Earth’s gravitational grip, the mummichog, Fundulus heteroclitus. You can find it here. They published only the first half of the essay; the entire essay is below. 

A large mummichog, Fundulus heteroclitus, from the Great Marsh. 

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When you launch a human body into space, sometimes that body become sick with nausea and general disorientation in the first few days. After a time, the body is better. This is the space version of seasickness. Because gravity holds our feet to the ground, we humans basically move in two-dimensions on Earth. So it may not be surprising that when you launch our bodies into gravity-free three-dimensional movement in space that our stomachs lurch and our heads spin. In the 1970’s the National Association of Space and Aeronautics (NASA) wondered how zero gravity would affect fish, animals that moved in three dimensions on Earth. Does a fish get space sick? For this important aquatic mission, NASA needed a fish that required little care but could endure the stress of a space launch and time in space. NASA first considered the goldfish, but they were not tough enough. NASA instead chose a drab, humble minnow found in salt marshes called the mummichog, Fundulus heteroclitus. It is not a fish prized as bait or aquariums so it is not well known. But if you’ve ever waded in the Bay of Fundy in Canada or Chesapeake Bay or the Gulf of Mexico in the U.S. and saw schools of minnows darting between your legs, then you met the first fish in space.

On July 28, 1973 at 7:11 a.m., the engines on the Saturn 1B rockets fired and the ground of Cape Canaveral, Florida, trembled. As the space shuttle lifted, the thrust pressed three American astronauts – Alan Bean, Owen Garriott, and Jack Lousma – into their seats. It also pressed the world’s first aquanauts, two juvenile fish and fifty fish eggs, against the walls of their small plastic aquariums. The rockets launched the astronauts and aquanauts into space for the second manned mission for Skylab (a mission confusingly called Skylab 3), the first scientific laboratory to orbit Earth.

When the two juvenile fish arrived at Skylab, they swam in elongated loops as though they were the spinning hands of a Salvador-Dali created clock. Without gravity the fish didn’t know which way was up. 

On the third day, the fish swam in regular patterns, always with their backs towards the interior lights of the Skylab. In many animals, including the two-legged kind that build rockets, gravity tugs on special cells in the inner ear and tell the animal which way is up (away from gravity). This is called the vestibular righting response. Without gravity to tug on their inner ears, mummichogs relied on artificial light to tell them what direction was up. Using fish logic this is reasonable. The sun never shines from bottom of the ocean.

Looping appeared to be the fish’s version of space sickness. Humans, like fish and other animals, rely on our inner ears for balance and orientation. When ocean waves or lack of gravity disrupts our signals, we become disoriented and often ill. As the mummichogs looped, the astronauts vomited. As the urge to vomit subsided in the astronauts, so too did the urge to loop in fish. By the fourth day in space, both human and fish had found their bearings. The fish swam in their small, plastic aquariums in space as though they had been there the whole time.

Would the unhatched fish be space sick and loop when they were born? The astronauts found out by their third week on Skylab, when 48 of the 50 eggs hatched. These tiny mummichogs did not loop. They immediately followed their older cousins and used the light for orientation. The fish fry having learned the up-is-where-the-light-comes-from-trick as embryos. Only when the astronauts shook the aquarium did the fish fry, apparently disoriented, began swimming in loops, only to return to swimming with their backs to the light.

I am a saltmarsh ecologist and know the mummichog well. It does not surprise me that the mummichog was the first fish in space. For the mummichog, space is only the next logical step for a fish that has tried to conquer land.

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On a summer day 30 years after mummichogs become the first fish to swim in space, I found a female mummichog – just barely longer than my middle finger, which is large by mummichog standards – laying in the grass. Abandoned by the tide, she was as stoic as sea-glass. Death will do that to you. I picked her up and she jumped out of my hand. I startled, not expecting a dead fish to be so agile. I picked her up and marveled about how far she was from the water: at least 100 meters, what must be kilometers in fish-distance. I looked at the tacky-skinned fish in my hand. A tough and adventurous survivor. I walked to a nearby pond and drop her in. She swam away as though she’d been there the whole time.

I was in the Great Marsh in Massachusetts. At low tide, the Great Marsh exposes its broad mudflats. In tidal creeks, the water may be shallow as a big toe is deep. In the rivers and bays, water may be only deep enough for small jon boats. During this time mummichogs and other fishes and shrimps wait in what crowded pockets of water they can find. Competition for food is intense. As the tide rises into the rivers and creeks, mummichogs who have been waiting in the deeper waters of the subtidal, follow the leading edge of the water in a crowded, confused mass. In fact, the name ‘mummichog’ is a Narragansett word meaning ‘going in crowds.’ As the creeks and rivers fill, the crowded fish twist their bodies as they bite the mud for small snails and worms. On the larger spring tides the water overtops the marsh and pushes into the expansive, grassy marsh. Here the fish spill into the marsh and spread out an army raiding a village. The grasses offer a menu not available in the muddy creeks and rivers: insects and spiders and small crustaceans. A fish who takes advantage of this easy protein grows faster than those that remain in the muddy creeks and rivers.

A flooded marsh is a land available to any fish willing to use it. But a fish can get greedy and forage far from the safety of a river and lose track of time and tide. This greedy fish can be trapped in a net of interwoven grasses and dilly-dallying. A fish that can breathe air survives. A fish that can’t, won’t.

Ever since the first fish, which didn’t really look like a fish, found itself in the Cambrian ocean 500 million years ago, it had to occupy a niche, that space in the world where it can make a living. It’s not always a perfect fit. Some fish, like the tuna, found their niche in the big, blue water. Some, like the deep-sea anglerfish, went to the big black water of the abyss. Some fish found themselves pushed against a new habitat, one strange to those with fins and gills, land.

Over time, fish watched the crustaceans conquer this new habitat, which gave them a roadmap to do the same. The first step? Learn to breathe air. The ancestors of the mummichog developed a gill that drew oxygen from both water and air. Mummichogs have retained this ancestral trait, which is why after any given spring tide in the warmer months, it is not uncommon to find the grasses of the salt marsh sprinkled with these finger-length fish. A mummichog can withstand a land no longer underwater if there is just the slightest bit of moisture to wet its gills. In this way, a mummichog can make do on regular air until it is rescued by the following tide. I have accidentally left a small mummichog at the bottom of a bucket with so little water that it lay on its side. The next day it did not complain and when I plopped it into an aquarium it swam as though it had been there the whole time.

Mummichogs can be stranded not only on land, but also in water. Mummichogs take refuge from the snapping jaws of stripers and flesh-shredding teeth of blue fish (Pomatomus saltatrix) in the ponds that pock the marsh. These ponds are only flushed during the spring tides of the new and full moons. In the interim, the oxygen levels in these ponds, particularly in the summer, can plummet to nearly zero. Most other fish species die. The mummichog gulps at the water’s surface and survives.

Mummichogs use their intertidal life to incubate their eggs in the safety of grass blades and shells high in the intertidal. During the spring and summer months, a female mummichog may lay her clutch high on grass stems during the highest spring tides. As the eggs are cradled in the crook of a grass blade, they are well above the ebb and flood of hungry mouths. The eggs develop slowly and will persist in even the strongest of summer swelters. Once the sea rises enough to wet them, possibly even a month later, big-eyed and translucent fry emerge and swim away within minutes. This habit of egg-laying and hatching is so coded in the mummichog’s genes that eggs never exposed to air do not hatch.

Terrestrial life began first as an aquatic one and then an amphibious one. Intertidal fish like the mummichog conquered the first challenge of an amphibious life, air breathing. Conquering land required, quite literally, another step. The first animal with a bony skeleton to crawl from the water to see the trees and find dry soil under it, was possibly the recently found fossil, Tiktaalik. This fossil is commonly called the ‘fishapod’ because it looks like a fish flattened from the top and bottom that has fins like short, stubby legs. Among evolutionary biologists, it is a most famous and celebrated fish. The mummichog is not a jealous fish, but it may take some satisfaction in knowing that while anyone can walk to an east coast salt marsh and admire a living example of the first fish in space, one has to go to a museum to see the now extinct Tiktaalik.

Fish are not supposed to live on land. Just as humans aren’t supposed to live in space. Yet today we find fish that can live on land, even if only for a little while just as we can live in space, if only for a little while. In the halls of NASA and living rooms of dreamers, we talk about living on Mars, an inhospitable planet compared to our own. Yet we hope to conquer and inhabit this planet. To make it our own. This sense of exploration and colonization is not a strictly human condition; if we look back far enough we can see it’s in our fishy genes.

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