How to Discover a New Species of Fish, by the Academy of Natural Sciences of Drexel University

By Academy of Natural Sciences of Drexel University

How to Discover a New Species of Fish by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Meet the Author

This is Mark Sabaj Perez, interim curator of fishes at the Academy of Natural Sciences of Drexel University in Philadelphia.

Fishes in a Pan by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Fishes in a Pan

Scientists, specifically taxonomists, discover new species in two different ways. One way is by studying plant and animal specimens at the Academy of Natural Sciences and at other museums. The Academy’s collection of more than 18 million specimens constitutes an archives of life. Each specimen is like a book. The more the taxonomist reads and compares one specimen to others, the more he or she is able to distinguish a known species from one not yet discovered.

Expedition Team by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Expedition Team

The second way taxonomists discover new species is through fieldwork at places unexplored or poorly sampled. The following images are from expeditions to the Xingu River, Brazil, an Amazonian tributary that was poorly sampled until recently. Funded by the National Science Foundation, the so-called iXingu Project was jointly led by Mark Sabaj Perez, the author; Lúcia Rapp Py-Daniel of the Instituto Nacional de Pesquisas da Amazônia, Brazil, and Leandro Sousa of Universidade Federal do Pará, Campus de Altamira, Brazil. In addition to yielding valuable new museum specimens to study, the fieldwork documented the natural aquatic diversity of the Xingu River prior to its disruption by Belo Monte, the world’s third largest dam complex.

Trawling to Sample Habitats by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Trawling to Sample Habitats

Taxonomists employ a variety of gear and techniques to sample the different habitats where fish live. Here we are using a net (submerged) that opens between two wooden doors (exposed) when dragged along the river bottom. Trawling yields species exclusive to the depths of large river channels, like the nearly blind knifefish and banjo catfish on the next two pages.

Knifefish catfish, Orthosternarchus tamandua by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Banjo catfish, Aspredo aspredo by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Banjo catfish, Aspredo aspredo

Aspredo eggs incubate while attached to the underside of the mother.

Using Baited Long Lines by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Using Baited Long Lines

Taxonomists also use baited long lines to sample large river channels. The line has many hooks and is set overnight in the channel. Long lines are effective for collecting large channel dwellers like the following migratory catfishes.

Tiger Shovelnose catfish, Pseudoplatystoma punctifer by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Goliath catfish, Brachyplatystoma capapretum by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Red-tail catfish, Phractocephalus hemiliopterus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Sampling with Gill Net by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Sampling with Gill Net

Taxonomists sample the calm margins and backwaters of large rivers with gill nets, which are checked throughout the day and night. Gill nets are effective for snaring deep-bodied fish like pacus and piranhas in the family Serrasalmidae.

Pacus, Myleus rhomboidalis by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Pacus, Myloplus rubripinnis by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Piranha, Serrasalmus rhomdeus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Ripsaw catfish Oxydoras niger by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Ripsaw catfish Oxydoras niger

Large gill nets are effective at catching channel dwellers like this ripsaw catfish. Its common name comes from the row of bony plates along its sides, each with a central thorn pointed toward its tail.

Red-bellied piranha, Pygocentrus nattereri by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Red-bellied piranha, Pygocentrus nattereri

Smaller gill nets can be set around specific habitat types such as a stand of water hyacinth. Fishes that school and feed under the vegetation, like this red-bellied piranha, become trapped in the net when they exit such habitats.

Stingray, Potamotrygon motoro by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Stingray, Potamotrygon motoro

Sandy beaches are best sampled with large bag seines pulled by hand. The best time to sample beaches is at night when many fishes move into the shallows to feed in the cover of darkness. Examples are freshwater stingrays and drum. Others, like the knifefish, rise up from their daytime retreats in the sand.

Drum, Pachyurus junki by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Knifefish Gymnorhamphichthys by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Cast-netting by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Cast-netting

Among the most difficult habitats to sample are large river rapids. One effective technique is cast-netting. Lead weights surround the perimeter of the circular cast net. They quickly sink to the bottom when thrown, trapping swift-water fishes like Leporellus vittatus and Leporinus fasciatus, two colorful members of the family Anostomidae.

Leporellus vittatus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Leporinus fasciatus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Using Hand Lines by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Using Hand Lines

Hand lines are another good way to sample large rapids, particularly deep swirling pools where large predatory fishes lurk during the day. Examples are peacock bass and sabertooth characin.

Peacock bass, Cichla melaniae by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Sabertooth characin, Hydrolycus armatus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

New pacu, Tometes kranponhah by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

New pacu, Tometes kranponhah

A specialized technique for sampling rapids is with bow and arrow or a homemade spear-gun. Deep bodied fishes like this new pacu turn on their sides to swim past shallow rapids. That makes them easy targets for a skillful shot.

Fishing Gaff by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Fishing Gaff

Another specialized technique employs the fishing gaff, essentially a large hook lashed to the end of a sturdy pole. The gaff is used to catch electric eels in shallow, quiet backwaters. The eels must surface to breathe air. The trick is to gaff the eel when it rises and pull it to shore without being shocked!

Electric eel, Electrophorus electricus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Catfish, Helogenes marmoratus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Catfish, Helogenes marmoratus

Streams are often sampled using small seines tied to brails pulled between two people. The seine can be set downstream of a particular habitat, like a submerged woody snag. The habitat is kicked and overturned, startling resident fishes into the net which is then lifted out of the water. Examples of fishes caught in this small blackwater stream are the catfish Helogenes marmoratus and tetra Hyphessobrycon heterorhabdus.

Tetra, Hyphessobrycon heterorhabdus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Dwarf cichlid, Apistogramma agassizii by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Flooded Forest Refuge by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Flooded Forest Refuge

Other habitats are only available in the high water season when the river floods its banks into the surrounding forest. Many fishes, including the arowana and tiger shovelnose catfishes, reproduce during this time, and the flooded habitats provide refuge for their young to mature.

Arowana, Osteoglossum bicirrhosum by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Hand-picking Fishes by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Hand-picking Fishes

The clear waters of the Xingu River provide ample clarity for diving and hand-picking fishes, especially plecos, an archetype of the tropical fish hobby. Ornamental fishermen carve slender pointed sticks to pin and grab or coax plecos from their hiding places in rocky crevices.

Pleco, Ancistrus ranunculus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Pleco, Hypancistrus zebra by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Dani the Fisherman by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Dani the Fisherman

For centuries taxonomists have relied on the skills and expertise of local fishermen. They know the river, specifically where, when and how to fish for particular species. Dani, shown here with his son, is an ornamental fisherman from Altamira. He collects fishes, especially plecos, to sell to the tropical fish trade. Prior to sale, the plecos are kept in wooden coffins submerged in the river near his home.

Pleco, Scobinancistrus aureatus by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Pleco, Panaque armbrusteri by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Fish Specimens Storage and Study by Mark Sabaj Perez/ANSAcademy of Natural Sciences of Drexel University

Fish Specimens Storage and Study

Our expeditions to the Xingu River have yielded thousands of new specimens to study at the Academy of Natural Sciences and at other natural history museums in the U.S. and Brazil. After the specimens are sorted into jars, identified and cataloged, another expedition beckons.

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
Explore more
Related theme
Natural History
The beautiful, the dangerous, the endangered. Up close.
View theme
Google apps