When I hear ‘electric fish’ I think about a species that has the capacity to sting others using an electric current. But not all electric fish emit a current that is dangerous. In fact, there are also weakly electric fish that do not use their electricity for defence, but rather, to communicate, navigate, and locate prey.
Currently, I’m working at Lake Nabugabo, Uganda, a small satellite lake of Lake Victoria. Last week, I put aside my interest in mercury contamination and spent a day working with another member of my research team. Tyler Moulton is a student based out of the Chapman and Krahe labs at McGill University, who studies the ecology of four different species of mormyrids— African weakly electric fish—present in this area.
One of the interesting things about mormyrid electric organ discharges (EODs) is that their signal properties are species specific. This is convenient, because the fish are often impossible to catch in the dense vegetation they inhabit.
Using these electric fish’s unordinary means of communication, Tyler is able to use an unordinary method to find them. In the above picture, Tyler is holding a stick into the water on which there are a pair of electrodes. These electrodes can detect the EOD of the fish and then relay them to a speaker and recorder. By simply recording EODs in the field and analyzing them using a custom written computer program, Tyler is able to determine which species are present in which habitat.
The Chapman/Krahe labs are also interested in the effects of hypoxia on these fish. Hypoxia, or low available oxygen, occurs in a number of different environments and leads to a panoply of interesting adaptations. In some of the region’s electric fish, individuals living in hypoxic environments like dense swamps, tend to have larger gills and reduced brain size. These changes are thought to help the fish to increase their intake of oxygen while reducing their oxygen demand. Some individuals also have the capacity to restrict the signals they emit, which may be a behavior that reduces energy expenditure in this extreme type of environment. This is a question that Tyler is interesting in further investigating.
To be able to study these questions, Tyler not only needs to be able to find, but also catch some of these fish. Curious about this “electric fishing”, I accompanied Tyler and Lake Nabugabo Field Station manager, Dr. Dennis Twinomuguisha into the field one day to see how exactly all this works.Using his electrode and speaker setup Tyler listens to the underwater world to see if any electric fish are present. Once they are located, the chase begins. Dennis will attempt to catch the fish hiding under the dense vegetation using a dip net.
For further information and future developments on this research you can visit Dr. Lauren Chapman and Dr. Rudiger Krahe’s websites (http://biology.mcgill.ca/faculty/chapman/, http://biology.mcgill.ca/faculty/krahe/).
More fishy tales, soon to come!