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Joe Szczebak

The clownfish and its anemone partner. The clownfish is named after its coloring and clumsy swimming.



Nemo after dark: Researchers discover night-time secrets of clownfish

by Elspeth Lodge
Feb 28, 2013

 Joe Szczebak

This video shows behaviors exhibited by clownfish among sea anemone tentacles at night, including fanning to supplement the oxygen of the anemone. The video was shot at the Marine Science Laboratory at Auburn University in Alabama.

Thanks to Pixar’s “Finding Nemo,” the mutually beneficial relationship between the clownfish and its anemone animal host is a popular research topic. But until now the relationship between the two at night has gone mostly unexplored.

Auburn University researchers in Alabama are shedding new light on the popular clownfish, also known as anemonefish, and their relationships to their anemone hosts at night.

 Joe Szczebak, former Auburn University student, and Nanette Chadwick, his master’s thesis adviser and a biology professor, report in the current issue of the Journal of Experimental Biology that clownfish fan their anemone hosts at night by moving their fins back and forth and that this motion supplements the anemones’ oxygen supply.

“Previous literature states that clownfish remain generally inactive at night aside from the occasional switch or wiggle,” said Szczebak. “Our study found that anemonefish collected both from the wild and in captivity spend the majority of the night in some form of motion.”

Anthony Mistretta, owner of Ocean Design Aquarium in Chicago’s Northwest Side, said he was aware of that clownfish stay busy at night by observing his own fish: “At home I used to have a tank with three clownfish and an anemone,” said Mistretta. “The clownfish was always moving in the anemone at night.”

George Parsons, director of the fishes department at Chicago's Shedd Aquarium, said the discovery that clownfish move at night doesn't surprise him either. He said he's noticed that they're a little less active at night, but that they still secrete water currents around the fish. This is the first study that he's seen that actually correlates the movement with oxygen production.

"I won't say that I suspected it," Parsons said of the discovery, "It just doesn't surprise me."

He said anemones don't have specific organs that extract oxygen, so they rely on the sloshy water moving back and forth to get all of the oxygen they need.
The larger the anemone, the more cells there are, and the more oxygen is needed. Clownfish tend to make their homes in larger anemones, Parson said.

He said the discovery also shows another reason why the anemone tolerates the fish living inside it, other than helping to fend off its predators.

 Szczebak agrees that the observation that clownfish move among the tentacles of their anemones at night is “by no means novel.” However, that specific nocturnal behaviors by clownfish appear to be intentional and triggered by physical contact with their anemone is a new discovery and was not yet documented by scientists.

Now, however, the fact that clownfish move at night within their hosts and that this movement has a specific purpose, to benefit its host, is documented on paper, thanks to scientific research that began in 2010.

From scuba diving in the Red Sea to working in a lab at Auburn University, Szczebak and Chadwick delved into an area of the relationship between clownfish and their anemone hosts that scientists have barely touched upon with their research.

Chadwick had a three-year grant through the National Science Foundation, which allowed her travel to Jordan and the Red Sea to conduct population dynamic and physiology research on clownfish and anemones.

In 2010, Szczebak joined Chadwick on the third year of her grant, in Aqaba, Jordan, for three weeks of research.

“They had been doing some physiological research where they were collecting respiration rates of the organisms,” Szczebak said. “And it got me thinking about how the relationship between them [the fish and the anemone] may affect their respiration rate or how they breathe. This was plausible because coral reefs can actually become pretty void of oxygen at night.”

During the day, photosynthetic microalgae within the tissues of corals and anemones photosynthesize, which produces oxygen, but at night photosynthesis stops and oxygen levels drop.

“Everything is respiring and that mixed with low flow can create zones of low oxygen that these fish and anemones have to deal with,” Szczebak said.

“They’re locked to their host. So, if the anemone gets anoxic, they can’t go anywhere. I figured that there may be an opportunity here. That this relationship may have some physiological ramifications at night, particularly related to oxygen availability.”

In the Red Sea there are lots of rules about diving at night, so Szczebak said he couldn’t go out on the reefs at night. However, he was able to collect specimens during the day and bring them back to a lab where he simulated nocturnal conditions.

Szczebak continued his research for a year and a half at Auburn after the trip to Jordan. He graduated in 2011 and now works for a company that designs and installs aquariums.

“He spent long nights filming these fishes and measuring oxygen is not easy,” said Chadwick. “I would say he’s an unusual student, not every student could do this.”

Szczebak measured their respiration rates when they were together and when apart through a process called flow-through respirometry.

In this process, the animal is put in a closed container and water is passed through. Szczebak measured oxygen levels before and after the animal entered the container, and measured the difference between the two measurements to see how much oxygen was consumed in the chamber. He saw how the net respiration changed when they were together versus when they were apart.

“While the study found that the fishes behavior at night seems to modulate the water flow through their anemones, right now its unclear if that’s the actual intended behavior of all that nocturnal activity,” said Szczebak. “They could be doing it for another purpose and this water motion might just be a secondary benefit.”

It was a symbiosis that was at first thought to be purely a protection symbiosis in which the clownfish protected the anemone and the anemone protected the fish.

In recent years researchers have found that there are more layers to the symbiosis than previously thought.

For example, Szczebak and Chadwick both mentioned that the waste that clownfish excrete actually fertilizes the algae inside the anemone and serves as an energy source for photosynthesis. The anemones that host clownfish have higher sustainability, higher growth rates and they achieve large sizes. They are all together healthier because they are fertilized by their fish, Szczebak said.

The research so far shows just how intimately connected the anemonefish and its host is and how interdependent and fragile coral reef ecosystems are, Szczebak said.

Parsons said that an interesting future study could concentrate on whether the clownfish senses when the oxygen level is dropping of the anemone, and whether that affects when the fish moves.