Chapter 1: Nets, traps and contraptions make up material used to collect electric fish

In preparation for the expedition down the Negro River in search of fish of the order Gymnotiformes, researchers gather more than 200 kilos of equipment and supplies for detecting, collecting and storing specimens.

By André Julião, from Manaus  |  Agência FAPESP – The day an expedition leaves is part of a long process that begins at least a few months before. By the time the vessel Comandante Gomes leaves its moorings at the Port of Panair in Manaus (capital of the Brazilian state of Amazonas), the researchers, technicians and students of the DEGy Negro River Expedition have already planned routes, organized equipment and supplies, and hired local support teams.

Agência FAPESP followed part of the preparation and the entire expedition, which lasted two weeks and went up the Negro River from Manaus to Santa Isabel do Rio Negro. The reports make up the Field Diary – Negro River series (see all the episodes at: agencia.fapesp.br/en/field-diary).

“Preparation is essential for the work to go well and for us to get the most scientific benefit from the expedition,” explains Osvaldo Oyakawa, a research support technician at the Museum of Zoology of the University of São Paulo (MZ-USP), who coordinated the work.

The DEGy Negro River Expedition was part of the “Diversity and Evolution of Gymnotiformes (DEGy)” project, supported by FAPESP.

On the plane with the researchers were nets, traps, sieves, sonar, GPS, ropes, field sheets to record each sample, an aquarium, tweezers and scissors to collect tissue samples, and gloves and plastic microtubes to store fish samples.

A total of about 100 kilos of material was checked in at Guarulhos International Airport on February 18.

In Manaus, formaldehyde, alcohol, nets, sieves, water tanks, aerators to keep fish alive, life jackets and tool kits totaling more than 100 kilos left the Federal University of Amazonas (UFAM) and the National Institute for Amazonian Research (INPA), partners in the project.

With everyone on board, small groups of researchers prepared the material for specific collections according to their scientific interests. Carlos David de Santana, a researcher associated with the Smithsonian Institution’s National Museum of Natural History in the United States, and Raimundo Nonato Gomes Mendes Júnior, an environmental analyst at the Chico Mendes Institute for Biodiversity Conservation (ICMBio) and a doctoral student at MZ-USP, made the final adjustments to the equipment used to detect poraquês and sarapós, as the electric fish are better known.

“We use a device that detects and amplifies the electrical signals emitted by the fish, whose data are transmitted and analyzed by software. We can observe variations in the amplitude and shape of the electrical wave, as well as measure the frequency and duration of the electrical discharges emitted by the poraquês and sarapós,” explains Mendes, who, although born and raised in the Amazon, was on his first expedition on the Negro River.

Preparations

In another corner of the boat, overlooking the uninterrupted forest on both banks of the river, Thiago Loboda, a postdoctoral researcher at MZ-USP with a scholarship from FAPESP, and Rubia Machado, a doctoral student at UFAM, prepared the longline, a set of hooks that would spend the night at the bottom of the river to catch rays.

Loboda is studying the morphology of freshwater ray species belonging to the family Potamotrygonidae to identify common traits among the different genera. “Most studies compare the members of this group using only molecular characters, so we want to consolidate that information with morphological characteristics,” he says.

More than Gymnotiformes, the expedition is an opportunity for researchers to collect other groups that occur in the tea-colored waters of the Negro River basin.

With 420 microtubes in his luggage, Machado intends to collect samples of the esophagus, stomach, pancreas, liver and muscle of three species of rays found in the Negro River basin for his research on the morphology and physiology of the digestive system of this group of fish.

In São Paulo, Laura Donin, a doctoral student at MZ-USP, prepared hundreds more of these plastic tubes, labeling each one with the proper identification and adding alcohol to preserve the samples. Liters of formaldehyde waited in a box in the corner of the boat.

When forage fish were caught with sieves in the creeks, small and large electric fish became entangled in the nets thrown up on the beach and in the trawl pulled by the boat, and the rays were hooked by the longline or collected with the puçá (fishing gear used by riverine communities in Brazil, mostly for catching crabs), everything was ready for the removal of tissues and the preservation of whole animals. The expedition had only just begun.

Also participating in the expedition from MZ-USP were Vinicius de Carvalho Cardoso, who is doing his master’s degree, and Jonatas Santos Lima Pereira, who also has a master’s scholarship from FAPESP.

The research team included Angela Zanata, a professor at the Federal University of Bahia (UFBA), and Lucia Rapp Py-Daniel, a researcher at INPA. The crew included ten other people.

The episodes of the Field Diary – Negro River series can be viewed at: agencia.fapesp.br/en/field-diary.