A question that’s often baffled scientists is how certain species of fish can sometimes appear—and even proliferate—in isolated bodies of water not previously known to harbor them. A new study has demonstrated that the most unlikely explanation might actually be correct: It’s possible they fell from the sky.
Specifically, from the rear end of a swan. A study in the journal Ecology by researchers at the Unisonous University in Brazil found that killifish eggs can, in rare cases, survive being swallowed by swans, enduring a journey through their digestive tracts before being excreted out. This kind of fecal public transportation system explains how killifish can pop up in ponds, flood waters, and other water bodies that would seem an unlikely place for species to suddenly appear.
After discovering that some plants could survive being ingested and then flourish in swan poop, researchers took notice of a killifish egg present in a frozen fecal sample. They set about mixing two species of killifish eggs into the food supply of coscoroba swans living in a zoo. After waiting a day, they collected the poop and dug in looking for the eggs.
Of the 650 eggs they estimated to have been ingested by the swans, about five were left intact. Of those, three continued to develop. Two died of a fungal infection, but one survived, enduring 30 hours in the gut and hatching 49 days after being excreted.
Because killifish eggs have a thick outer membrane, or chorion, they stand a chance of coming through the digestive tract of an animal intact. Not all of what a swan ingests will be absorbed; their stomachs are built to extract nutrients quickly and get rid of the whatever's left so the birds can eat again. In rare cases, that can mean an egg that can go on to prosper.
Not all fish eggs are so durable, and not all fish are quite like the killifish. Dubbed the "most extreme" fish on Earth by the BBC, killifish have adapted to popping up in strange environments where water may eventually dry up. They typically live for a year and deposit eggs that can survive in soil, delaying their development until conditions—say, not being inside a swan—are optimal. One species, the mangrove killifish, can even breathe through its skin. When the water recedes, they can survive on land for over two months, waddling on their bellies or using their tails to "jump" and eat insects. A fish that can survive on dry land probably doesn't sweat having to live in poop.
The researchers plan to study carp eggs next to see if they, too, can go through a lot of crap to get to where they’re going.
New Words and Phrases to Learn
Baffle: if something baffles you, you cannot understand or explain it at all
(Collocations)
- A puzzled/ baffled/ bewildered expression
(Example)
- The question baffled me completely.
Proliferate: if something proliferates, it increases quickly and spreads to many different places
(Example)
- Computer courses continue to proliferate.
Harbor: (1) to keep bad thoughts, fears, or hopes in your mind for a long time. (2) To contain something, especially something hidden or dangerous. (3) To protect and hide criminals that the police are searching
(Example)
- Sinks and draining boards can harbor germs.
Swan: a large white bird with a long neck that lives in rivers and lakes
Ecology: the way in which plants, animals, and people are related to each other and to their environment, or the scientific study of this
(Collocations)
- Fragile ecology
- Plant/ animal ecology
- Marine ecology
- Rainforest ecology
(Example)
- The natural ecology of the earth
Killifish: a kind of fish
Swallow: to make food or drink go down your throat and towards your stomach
(Collocations)
- Hard to swallow
- Swallowed hard
- Swallowed nervously
- Swallow … whole
Endure: (1) to be in a difficult or painful situation for a long time without complaining
(2) to remain alive or continue to exist for a long time
(Synonym) tolerate, put up with something, accept, stand/ bear, live with something
Tract: a system of connected organs that have one main purpose in a part of your body
(Collocation)
- The digestive/ reproductive/ urinary etc. tract
Excrete: (formal) to get rid of waste material from your body through your bowels, your skin etc. (= secrete)
Fecal: related to solid waste material from the bowels => (Noun) feces
Pop up: appear suddenly
Pond: a small area of fresh water that is smaller than a lake, that is either natural or artificially made
Ingest: to take food or other substances into your body (= digest)
Prosper: if people or businesses prosper, they grow and develop in a successful way, especially by becoming rich or making a large profit
Dub: to give something or someone a name that describes them in some way (= label, name)
Deposit: (formal) to put something down in a particular place
(Noun) a part of the cost of something you are buying that you pay some time before you pay the rest of it
(Example)
- A deposit of 10% is required.
Belly: stomach, abdomen
Crap: very bad
(Example) (1) a crap film
(2) I’ve had such a crap day.
(3) I’m really crap at tennis.
