Highlighting Biodiversity: Freshwater Fishes in Equatorial Guinea

As the Academy celebrates biodiversity — the remarkable, beautiful tapestry of life on Earth — this year, we are delving into some of the fascinating locations our scientists have visited in the region and across the globe to study and help protect our planet’s phenomenally diverse and incredible species. 

The wondrous natural beauty of Equatorial Guinea. Justin Jay/BBPP

The Mainland and the Island 

With dense canopies, soaring mountains and bubbling streams, Equatorial Guinea is composed of two wonderfully biodiversity-rich locations — the mainland Río Muni on the west coast of Central Africa and its islands, Bioko and Annobón.  A long chain of volcanoes extends southwest from the mountains in continental Cameroon into the Gulf of Guinea, where it gives rise to the islands of Bioko, Príncipe, São Tomé and Annobón. Bioko is actually much closer to Cameroon than the continental part of Equatorial Guinea.

Bioko has tropical monsoon climate that provides plenty of freshwater to its many streams. These streams are home to two types of fishes: those that live along coastlines and commonly move upriver into freshwater (amphidromous fishes); and those that are restricted to freshwater (continental fishes).  

The origin of Bioko’s freshwater fishes is somewhat of a mystery. Since botanists estimate that populations a flowering plant species (Lobelia columnaris) on Cameroon and Bioko were separated 1.54 million years ago, ichthyologists, in a similar fashion, suspect the freshwater fishes are most closely related to those of nearby Cameroon. Whether they have been isolated from their continental counterparts for a longer or shorter timespan has yet to be determined. 

Old Fish, New Fish 

With funding from Academy benefactors Daniel and Patricia Fromm, a team of Academy naturalists — Collection Manager of Ichthyology Mark Sabaj, Research Associate Cecile Gama, Manager of Animal Programs and wildlife photographer Anwar Abdul-Qawi, Curatorial Assistant and Fulbright Scholar Daouda Njie and Director of the Bioko Biodiversity Protection Program David Montgomery — conducted a two-week expedition to collect fishes. 

When looking for “new” species, Sabaj explains, it is important to know the “old” ones first. In 1863, for example, Dutch medical doctor and ichthyologist Pieter Bleeker (1819–1878) described a species of minnow, Enteromius camptacanthus, from Bioko but did not record which exact stream his specimens came from (or, the type locality). Since Bleeker did, however, publish a color illustration of his new species, the team knew what to look for among the fishes now inhabiting Bioko. 

The crew sampled three streams draining out of the northwest part of Bioko and found Enteromius in two of them. One of those streams was near the international airport west of Malabo, where they saw fishes scurrying in an open-top culvert along the parking lot. This stream held two species of Enteromius, E. trispilos (top left) and E. callipterus (not shown), neither of which resembled Bleeker’s illustration.  

Another nearby stream, less than 8 km as the crow flies, drained separately into the Gulf of Guinea. There they found an Enteromius that resembles Bleeker’s illustration in some ways (reddish fins) but differs in others (main stripe along body discontinuous, dorsal stripes lacking). The search continues. 

Exciting Scientific Discoveries 

After sampling Bioko, the group then traveled to mainland Río Muni to collect fishes in the Río Benito, the largest river system in the continental part of Equatorial Guinea. Fish specimens from mainland Equatorial Guinea are relatively scarce in museums, so this was an exciting development. 

The group caught the colorful Distichodus mbiniensis in the upper Río Benito and in the lower Benito, they were surprised to catch another species that resembles D. hypostomatus (below, bottom), a species not previously recorded from Equatorial Guinea. Their sampling is the first to document two species of Distichodus from the same river basin in the country, but further study is required to confirm such a fascinating discovery.  

Distichodus. Mark Sabaj/ANS

The team also found at least two other fish species never before reported from Equatorial Guinea — caught in the same seine haul! In the lower Benito, Sabaj spotted a specific type of habitat that serves as a daytime retreat for nocturnal fishes: an undercut bank with dense mats of submerged roots. Carefully inserting their nets beneath the roots and then with a few good shakes, the team lifted the nets out of the water and away from the bank.  

It was a success. They caught over 100 specimens representing four species of elephantfish. Mormyrids are a group of weakly electric fish endemic to Africa and related to North American hiodontids (mooneyes and goldeneyes).  

Mormyrids. Mark Sabaj/ANS

“As far as we can tell, two of the mormyrids from our net are new to the known fauna of Equatorial Guinea,” Sabaj explains excitedly. “These discoveries, and the species recently described by others working in Equatorial Guinea, show that more sampling is needed to fully understand the country’s fish fauna.” 

Respecting the Methods 

When collecting fishes in a foreign country, ichthyologists often seek out local fishermen for help. They know the best places and times to fish, and what type of gear and bait to use for particular species. On the banks of the Río Benito, the group met one fisherman with a woven basket full of airbreathing catfishes that he had caught the night before. He kindly sold Sabaj his catch — a fortunate turn of events, as they had no luck finding these elusive nocturnal catfishes during the daytime.

Highly successful and well-crafted woven baskets. Mark Sabaj/ANS

Overall, the two-week trip to Equatorial Guinea yielded 1,342 specimens now cataloged into the Academy’s phenomenal Fish Collection and available for study by the global community of ichthyologists. The specimens represent about 56 species and 21 families of mostly freshwater species. Also collected were 229 fish tissue samples for DNA studies. Brazilian ichthyologist Gabriel de Souza da Costa e Silva, with funding from Brazil, has already begun a postdoc with Sabaj at the Academy and will investigate the genetic relationships of catfishes from around the world — using specimens collected from this very trip.  

Catfishes. Mark Sabaj/ANS

The Future of the Region’s Biodiversity 

Equatorial Guinea, and Bioko Island, are some of the most unique biodiversity hot spots in Africa, especially important for rare endemic primates and nesting sea turtle populations. Many of the species thriving there, including freshwater fishes, are found nowhere else on the planet.  

These places are a small yet important piece of the larger central African rainforest system.  Because of their geographical size and unique history, documenting the astounding biodiversity found there and preserving as much of the remaining African forests as possible will be critical for mitigating  biodiversity loss and the effects of global climate change. 

Understanding, appreciating and conserving biodiversity has been at the core of the Academy’s science work since its founding in 1812. With 19 million specimens and counting, our collections are not only a window into the past, but also a critical tool for measuring the current and future health of all Earth’s species.  

During Biodiversity Year, join us as we bring our understanding of the natural world from the lab to City Hall and beyond, so that together, we are a force for nature. 

The team wanted to thank their generous hosts in Equatorial Guinea. Without their help, this trip would have been much less successful (if not impossible) and far less fun. On Bioko, they were supported by the Bioko Biodiversity Protection Program and were fortunate to have Elpidio Buelecope Sepa and Constantino Obama Bindang (among others) on their team. Juan Cruz Ondo Nze, a highly experience naturalist, and Jose Mari Edjang (their driver) deftly guided the crew on the mainland. Paulo Speller, Director of the Universidad Afro-Americana de África Central (AAUCA) kindly provided everyone with a place to stay on campus and access to the dining hall. AAUCA students and professors helped Sabaj and team sample sites in the upper Benito. Maximiliano Fero Meñé, PhD at the Universidad Nacional de Guinea Ecuatorial (UNGE) invited the team to lecture to his students and helped with permits. And finally, a big thanks to UNGE and INDEFOR-AP for authorizing the expedition. 

Written by Mark Sabaj, Collection Manager of Ichthyology at the Academy
Edited and modified by the Academy Editor

Featured Photograph of Bioko by Anwar Abdul-Qawi

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