Researchers find new killifish species in Kenya

NAIROBI ― A new killifish species, scientifically known as Nothobranchius sylvaticus, has been documented in seasonal swamps of Kenya’s ancient Gongoni Forest, research shows.

In a study published this month in the Zootaxa journal, scientists from Canada, France, Kenya and South Africa say the fish species’ survival is compromised by the severely restricted and declining habitat, which is part of the seasonal Mkurumudzi River in southeastern coastal Kenya.

N. sylvaticus, from the Latin phrase meaning “pertaining to the forest,” is also the first known killifish to persist in a forest and was sampled from the Gongoni Forest in 2017 and 2018.

Its iridescent blue scales, pronounced red markings on the head and vibrant fins set it apart from other Nothobranchius species. The killifish specimen has been deposited at the National Museums of Kenya in Nairobi and the comparative specimens at the Royal Museum for Central Africa in Tervuren, Belgium.

According to the study’s lead researcher, Dirk Bellstedt, professor emeritus of biochemistry at South Africa’s Stellenbosch University, in 2017, he was invited by Quentin Luke, a botanist with the National Museums of Kenya and a study co-author, to help in environmental monitoring of the Base Titanium mine in Kwale county near the coastal town of Diani Beach in Kenya.

“I have researched forest patch plants far down the east coast of Africa in South Africa and that is why I was particularly interested. On getting there, I noted there were ponds both inside and outside the forest. As I was also working on an all-Africa project on the fish genus Nothobranchius, I decided that this might be valuable to investigate,” Bellstedt tells Mongabay.

To his advantage, he had information about coastal Kenyan Nothobranchius species, shared with him by his colleague, Béla Nagy, a Hungarian zoologist based in France specializing in African killifish, specifically of the genus Nothobranchius, also co-author of the paper, who discovered intrepid Nothobranchius and has described many new species of Nothobranchius throughout Africa.

“I knew some [Nothobranchius] could be expected in the area. The [Base Titanium] mine requested that I assess the fish fauna in the Gongoni Forest area below the mine to assist them with their environmental monitoring,” Bellstedt says.

With waders, nets and buckets, he and his support staff began collecting fish samples. “I found [tiny] (1-2 cm) [0 .4-0.8-inch] individuals of the species, which were clearly Nothobranchius, but were not identifiable at species level. DNA sequencing and phylogenetic analysis of the Kenyan species revealed that it was not only a new species but also a completely new lineage for Kenya, in other words, a very special find from the Kenyan perspective,” Bellstedt tells Mongabay.

In 2018, they recollected adult specimens and assessed their morphology and found clear morphological differences from other Nothobranchius species occurring nearby, as a second line of evidence to prove that it was a new species.

“To conserve species, you have to know that they are present in an area and this study has established that this forest contains an endemic fish species, making it completely unique in Kenya. This species is an integral part of the region’s biodiversity and adds to the knowledge of the endemic species,” Bellstedt says.

The researchers say the Gongoni Forest, which stretches about 8.2 square kilometers (approximately 3.2 square miles), is more than 7.1 million years old and exemplifies the East African Mosaic, which combines savanna interspersed with forest patches that stretches from Pondoland in South Africa to southern coastal Somalia.

“The forest patch was always moister, and during arid cycles, savanna species may have died out, but this species did not. The African East coast contains regular forest patches from Somalia to South Africa, which contain many species of plants, animals and birds unique to each forest patch, and this is the first fish that was found to be unique to a forest patch. The age of the fish, as determined from the dated phylogenetic analysis, [indicates] the age of the forest patch. Thus, the age of a forest patch, a specific vegetation feature, is dated from the fish inhabiting it,” Bellstedt says.

According to Luke, the discovery points to the urgent need to conserve the forest patch and protect the species.

“Abstraction of water by the mine was a threat, but the mine completed its activities at the end of 2024, so this threat has now been relieved,” Bellstedt says, adding that there is a need not to allow human and agricultural encroachment on the forest patch, such as the abstraction of water on the southern border for crop cultivation.

Dario Valenzano, a biologist who researches African killifish and was not involved in the study, concurs that human actions like farming and mining could significantly harm the limited habitat of the killifish.

“They live in [tiny] areas where water supply is also intermittent due to droughts and this is already a threat to them. Kenya and Tanzania have the largest diversity and distribution of killifish species, and there is a need to protect them from extinction. We need to sensitize communities on their importance, and that they are fragile, so that they understand the need to protect them,” says Valenzano, who heads the Valenzano Research Group affiliated with the Leibniz Institute on Aging – Fritz Lipmann Institute in Germany.

According to Ashley Simkins, a zoology Ph.D. candidate at the University of Cambridge with research interests in endangered species, the protection of the species in its natural habitat is critical, as it highly depends on the habitat, including for key life stages such as egg development. “If this area is heavily degraded or lost, the species will likely go extinct. Some species are very tricky to breed in captivity, particularly if their ecology is poorly understood; as this is a new species, that may be the case. Given this, and any behavioral changes in captivity, it is preferable to try to facilitate breeding and population growth in their natural environment rather than relying on captive breeding,” Simkins tells Mongabay.

He is calling for the formal recognition of Gongoni Forest as a key biodiversity area and engaging of the local communities to explore the protection of the area to shield the species and its habitat. “As this is a small freshwater fish, assuming it has a high reproductive rate, protecting its habitat, through protected area designation or otherwise, should be sufficient to allow it to recover to natural levels and avoid further threats.”

Banner image: Researchers find a new killifish species, Nothobranchius sylvaticus, in an an ephemeral swamp in the Gongoni Forest Reserve in Kenya. Image by Dirk Bellstedt.

Citation:

Bellstedt, D.U., Nagy, B., Merwe, P.D., Cotterill, F.P., Luke, Q., & Watters, B.R. (2025). The description of a critically endangered new species of seasonal killifish, Nothobranchius sylvaticus (Cyprinodontiformes: Nothobranchiidae), a relict species from an East African forest refugium in south-eastern Kenya. Zootaxa, 5601(1), 86-108. doi:10.11646/zootaxa.5601.1.4

Credits

Ochieng’ Ogodo Editor

This story first appeared on Mongabay

This article is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.

You may republish this article, so long as you credit the authors and Mongabay, and do not change the text. Please include a link back to the original article.