SPEAKER 1: Did you know that there are fish that communicate and navigate using electrical signals? Professor Carl Hopkins of the Department of Neurobiology and Behavior will show us.
CARL HOPKINS: Did you know that this fish that I'm showing you is capable of generating electricity? There's a little battery in its tail. It's an electric fish from Africa. And I'm going to demonstrate that by taking the fish and putting it in this tank over here that has an electrode in it. And we're going to connect the electrode to a loudspeaker, so that we can hear the electric discharges.
So take the fish out, and put him over here in this tank. And then I'm going to turn the loudspeaker up so you can hear it.
And so those pulses that you're hearing are the fish using its navigation system, which is based on electrical pulses. to move around in the environment and find objects, and also to communicate with other fish of the same type.
So again, let me just remove the fish while you listen.
You can hear the clicks very clearly.
Take him out, no longer in contact with the water. You can't hear anything, because the discharges are not able to go through the air.
But in the water, you can hear just fine.
[? Isid ?] here is an undergraduate student, and he and I are going to demonstrate this next week when some freshmen students are coming to the lab to learn about what research is going on here at Cornell. So we hope to demonstrate these electric fish to them, and also to show not just the electric discharges, but to show the electroreceptors, which the fish have on the surface of their skin.
So we're here to do Explorations. Explorations is a program that was started about almost 12, 13 years ago by a graduate student teaching in the introductory biology course, BIO 101. And he thought, what does Cornell do best? Research. The freshman never got to see the faculty, except for the few teachers that they had in the big courses. So here we are. So now you get a chance to visit a lab. And we hope, this afternoon, that you can do a few of the procedures that we do during our research.
SPEAKER 1: The freshmen divided into three groups. One to work with Professor Hopkins, and the other two with Brian and Farrah.
CARL HOPKINS: And so you're asking what they detect normally. What they detect is other fish. They're very sensitive, and they are tuned, electrically tuned, to the frequency that's characteristic of the other fish.
SPEAKER 2: Yeah.
CARL HOPKINS: Now, when you zoom it, you may have to refocus.
SPEAKER 2: Yeah.
SPEAKER 1: The fish is temporarily paralyzed and held in those little plastic holder. The spots on the fish are electroreceptors. Here's a close up.
SPEAKER 2: The size isn't much, but--
CARL HOPKINS: You don't see that--
SPEAKER 2: I can tell the different colors.
CARL HOPKINS: You really have to look at it for a while.
SPEAKER 2: Oh, OK.
CARL HOPKINS: Because your brain has got to have time to figure out the different categories.
SPEAKER 2: Oh.
CARL HOPKINS: And then I want you to try to move it away from-- and you could see that the signal is coming from that pore. It really is a spike that's generated from the pore. And notice that the height of the spike is pretty constant. Doesn't vary. It's all or none. There are multiple cells within the organ, and they're probably firing right next to each other, producing two spikes. So that's why we see s doublet.
All right. Ismail, who's a freshman student-- a sophomore student, I should say, that I've known for one year at Cornell. And she's been working in the lab for about two months. And her project is to work on the same species of fish, but in the larval form. And what we're interested in is how the adult patterns of discharges develop over time in these very early stages of development.
ISMAIL: See these things? But generally, I'm looking at the interval, because I'm looking at it [? speed ?] [INAUDIBLE]. So once I calculate that, it'll give me the difference in intervals for all of the data points that--
SPEAKER 3: Oh, [? general. ?]
ISMAIL: Right. So if you make them more condensed, sometimes it's easier to see what the pattern is.
BRIAN: This is in MATLAB. So if you take CS 100M, it would be very helpful for pretty much any research, if you're interested in doing. Research. So I think the transition from JAWS into MATLAB is pretty easy. MATLAB's more forgiving than the JAWS. JAWS is a little bit harder at programming.
SPEAKER 1: This fish is in Brian's experimental tank. Two recording electrodes and a hiding tube are on the bottom of the tank. In back, with one end painted red, is a pair of stimulating electrodes. Brian can play back a recording of a male's electrical pulses.
BRIAN: I'm just recording directly this stimulus that I'm playing to the fish. So I want to make sure that I know what I'm playing to the fish, and when I'm playing it. So this just gets directly recorded through the camera. It will record a certain behavior, and that way you can just do counts with behaviors. So if you see the fish headbutt the electrode or something, you can just push a button and keep track of where you're at.
SPEAKER 1: Here is Brian's recording. Now the playback starts.
Watch what the first does. Now Brian reverses the polarity of the electrode.
Where's the fish now?
This is good evidence that the fish can detect the polarity of the electric field.
SPEAKER 3: Our breathing is automatic. We don't have to think about it.
SPEAKER 4: So, yeah, the fish discharge-- it's under a conscious control, if you will. They have descending inputs to modulate the rate of discharge. So let's say, for example, that some novel aspect of their environment-- let's say I stick my pen in there and start chasing the fish around. It has a novelty response. It actually increases that sampling rate of that discharge to get a better image of that novel feature. And then similarly, if it's swimming around with a girl fish, and they want to mate or something like that, they can actively display--
SPEAKER 3: OK.
SPEAKER 4: So they're consciously controlling. It's not like an automatic response.
SPEAKER 3: Right.
CARL HOPKINS: This is a nice demonstration of bioelectric activity, because students don't realize that the electrical activity in their nerves and muscles actually could get strong enough to go outside the animal. And these fishes are just excellent examples of that.
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Some fish use electric signals to communicate and to locate prey. Join Cornell professor Carl Hopkins, an expert on these fishes from the African Nation of Gabon, as he introduces a group of freshman biology students to his research on mechanisms and uses of electric communication among fish.
Hopkins is the 2009 recipient of the prestigious CALS Edgerton Career Teaching Award and a faculty mentor in Cornell's introductory biology Exploration Program. Students in the program choose a topic of interest and participate in the research, working with lab equipment and gathering data in the labs of some of the top researchers in the country.