Tag Archives: fish

Why These Fish Bully Other Fish–Into Breathing Air

[Two Clarias gariepinus catfish caught near Bogor, West Java in Indonesia. Image by W.A. Djatmiko via Wikimedia Commons and CC-BY-SA-3.0] 

There’s one in every school. These aggressive individuals go around pushing and biting their neighbors, goading them into risky behaviors–like breathing.

Several species of catfish, including the African sharptooth catfish (Clarias gariepinus), have both gills that take in oxygen from water and an organ called the “labyrinth” or “dendritic organ” that allows the fish to “breathe” air.

These catfish evolved to survive in warm, humid rivers–where oxygen levels in the water can drop dangerously low at night.  So while they breathe through their gills most of the time, the fish also have the option of swimming to the surface and taking a big gulp of air.

But, oddly enough, low oxygen levels don’t fully explain catfish’s breathing choices. For one thing, they tend to surface in groups.

Behavioral ecologist Shaun Killen of the University of Glasgow  wondered whether something in the social lives of catfish might be driving them to the river surface, so he teamed with catfish researchers at the Federal University of Sāo Carlos in Brazil to find out more.  

In the experiment, the scientists assigned the catfish to groups of four per tank and counted the number of air-breaths. They repeated the test at several different dissolved oxygen levels and then compared the group counts to how often the fish air-breathed while alone.

They found that fish breathed air more frequently when other fish are around, even when there was plenty of oxygen in the water.

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The Case of the Fish in the Flood

[A high flow event at Glen Canyon Dam in November 2013.  Photo by the Bureau of Reclamation via Flickr & CC 2.0 License.] 

Proposed Headine:

How an Invasive Species (Almost) Stopped a Flood

Proposed Dek:

“High flow events” or controlled floods are a key tool for managing the Colorado River. But what happens when an invasive fish gets in the way?

The Pitch:

Hi! While recently visiting Utah, I came across an interesting story about the Colorado River. Let me know if you’d be interested:

Is the threat of spreading an invasive species enough to justify canceling projects that help maintain the ecosystem? That’s the question facing resource managers at the Glen Canyon Dam on the Colorado River.

Last year, they had to cancel a controlled flood or “high flow event” because there were a large number of green sunfish in backwater sloughs just downstream of Glen Canyon Dam. They were concerned that opening the dam’s floodgates might wash the green sunfish downriver into the territory of an endangered fish species called humpback chub. However, controlled floods are crucial for releasing sediment that builds up near the dam and rebuilding shorelines and sandbars downstream in the Grand Canyon area. “When the Glen Canyon Dam was built, it blocked 90% of the sediment that was coming through the Colorado River,” explains Rob Billerbeck of the National Parks Service. “So it changed what used to be a red river to a clear river.”

Without the floods that carry sediment downstream, shorelines erode. But more water flow also means more risk of invasive fish spreading. This year, the green sunfish may cause the cancellation of a second flood. So far, Parks Services officials have dealt with the situation by killing and removing the invasive fish from the river system. The NPS and the Bureau of Reclamation are optimistic that they’ve “treated” all of the green sunfish and will be able to move forward with a controlled flood, but the issue of balancing the need to prevent invasive species’ spread with the need to rebuild sandbars and shorelines will likely be a recurring one. This year’s controlled flood will go forward on November 7th, but the green sunfish problem seems likely to come up again.

Although it’s primarily an environmental and resource management story, I think the philosophical hook of “dammed if they do, dammed if they don’t” (sorry; couldn’t resist the pun) that raises an interesting philosophical question: What happens when invasive species begin to take wildlife management decisions out of human hands?

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