Carp: Criminals or collaborators?

If you’re an average person in the US, and you think of carp, you might picture koi—the lovely multicolored fish often swimming around in little ponds in Asian restaurants and gardens. If you’re someone like me, who spends a lot of time thinking about human/wildlife interactions, you might think of the common carp, invasive in Australia, to the point that the government is considering giving them all herpes to control the population.

But a thing I didn’t think about? Rice.

Because it turns out that carp have been helping farmers in Asia raise their rice for centuries, a lovely form of mutualism that benefits, rice, carp, and people.

Humans have formed domestication relationships* with lots of grains. Wheat, emmer wheat (a more different wheat), millet, corn, oats, barley.

But rice? Rice is a bit different. It’s a wetland crop, and likes its feet wet, but only at very specific times. It’s planted in a dry field, that field is flooded a few inches, and then the water is drained before harvest. This method works well if you have the right irrigation, or the right combination of dry and wet seasons.

The problem is that lots of OTHER plants like a nicely prepared field, a nicely flooded field, and so on. But you know what else likes plants that grow in the water?

Carp! Carp is a catchall name for a bunch of species of fish in the family Cyprinidae, and includes grass carp, common carp, silver carp, crucian carp and a carp in a pear tree. These are all fish native to Eurasia, and plenty tasty. People have been raising them to eat in China since at least 400 BC, when someone named Fan Li wrote a guide to fish aquaculture, which described digging a pond, adding fish fry (as in baby fish, which are called fry, not fried fish, that would be a waste of a delicious meal), and selling or eating the results a few months later.

Historians guess that at some point, people had extra fish fry, had to put them somewhere and tossed them in the flooded rice paddies, and poof. The carp nibbled at the fresh growing weeds, leaving the more mature rice stalks alone. So the system developed, with farmers adding carp after the fields were flooded. These were fingerling carp, which could then be transferred elsewhere when they got big enough. Basically the rice field serves as a fish babysitting system. Bonus: fish poo makes good fertilizer.

No one is quite sure when the practice started, but certainly by the Eastern Han Dynasty (think: 100 AD ish) farmers were putting carp in their rice fields. We know because tomb excavations have found art of it. Little clay models of rice fields, and those rice fields had tiny clay carp!

There’s another method of doing this, and that’s using the carp to prepare the ground for the rice. Dig out a new field, flood it, and release the carp. Come back a year or two later, and the carp are big and delicious, and all the weeds in the new field are gone, and the soil is extra fertile from all the fish poo. That method was described in the Tang Dynasty (think: 900 AD).

People have continued to use both of these methods, and still do, throughout Asia (though during the Cultural Revolution, there was a moment in China where growing carp was considered to be unacceptably bougie. This did not stop people).

Keep in mind, it’s only in modern times that this system has been considered to be mutualistic, to be good for the rice and the carp and the people. The rice grow faster and better with more fertilizer and fewer dangers from disease and weeds. The fish grow better in artificial ponds with plenty of food and no predators. The humans grow better on rice and carp. Originally, it was just a nice way to get extra carp. But now we see it for what it is: A system where humans, carp, and rice all benefit together.

References

1. Renkui, C.; Dashu, N.; Jianguo, W. (1995). "Rice-fish culture in China: the past, present, and future". In Mackay, Kenneth T. (ed.). Rice-Fish Culture in China. Ottawa, Canada: International Development Research Centre. ISBN 0889367760.

Where have you been?

• I hope it’s reading The Chaos Machine, which is a book about social media, and how it’s changed everything about the way we communicate and even the way we think. Honestly I can’t recommend it enough, it’s made me see my online life in a totally new and honestly horrifying way.

• Scientists spent years taking all of these bass out of a lake in the Adirondacks. The result? Not FEWER bass. Just…smaller bass. Whoops.

• You might have been told to squish those spotted lanternflies. But…have you thought about why these invasive bugs are doing so well? Because the answer is that their preferred host, the tree of heaven, arrived before it did.

• If you wonder why everything feels so wrong, the answer is hypernormalization. “It’s reading an article about childhood hunger and genocide, only to scroll down to a carefree listicle highlighting the best-dressed celebrities or a whimsical quiz about: ‘What Pop-Tart are you?’”

• LOOK at this adorable little ancient reptile with his little BACK FAN! 

• An artist covers his canvases in flies. The flies eat sugar water with colors in it, and poop out…um….art. The result is honestly fascinating.

• Every heatwave you hear someone saying we should just learn to live with it, that putting up with heat is somehow more virtuous, or better for the climate. Sure, it’s better for the climate (though heating causes more climate change), but AC? It’s a matter of public health.

• This Roman mosaic was finally recovered, and my favorite thing about it is that in an effort to make the subject LESS sexual…they blurred the bare butt. With the result that the butt actually looks MORE BARE than before. I love it.

• This is brave, and really impactful. Scientists held a “science fair” in congress, showing off the work they were doing…before their grants were cancelled.

Where have I been?

• I’ve been on the “Now That’s What I Call Green” podcast, talking about science journalism careers, science in the US (um, yikes), and of course, pests!

• I was also on the Atlas Obscura podcast, talking about the book, and about which animals, if any, might actually earn their villain title.

• I wrote a feature about something that might light up your brain. Seriously. Did you know that cells produce photons as part of their metabolism? If we find out that cells can USE those photons, what would that mean?

• I also wrote a piece about how it is that Burmese pythons manage to break down even the BONES of their prey. They have special cells (ssssssspecial) that collect nuggets of extra calcium for their poo!

• And I wrote another piece that was just fun. This was about how dogs watch TV. While it’s actually about anxious responses or play responses, in my head now it’s clear that schnauzers are true-crime girlies, pomeranians are watching The Secret Lives of Mormon Wives, and pitties love The Bachelor.

• And of course it’s summer which means it’s time to SWEAT. We often think of sweat forming discrete droplets. But it turns out it’s more like a set of flat drops on the oversoaked sponge of our skin.

*I say “domestication relationship” and not “humans domesticated” because scientists now understand that domestication isn’t something we INFLICT on species. It’s a two-way street. The plants and animals we domesticate change, but so do we, and sometimes in extremely drastic ways!