By Xiluva Mathebula, Nkululeko Zuma, Albert Chakona
The Goukou galaxias (Galaxias sp. nov. ‘goukou’) is a fascinating small, cylindrical freshwater fish that grows up to 70 mm in total length. This unique fish possesses a semi-translucent body that reveals glimpses of its internal anatomy without the aid of specialised equipment or dissection. Its transparent nature serves a vital purpose by helping the fish blend seamlessly into their environment, and effectively camouflaging them from potential predators. Compared to the other Cape galaxiids, the Goukou galaxias has a conspicuously large eye, a distinctive narrow tail and an inwardly curved notch on its tail fin.
Habitat and movement
The Goukou galaxias thrives in moderately deep pools containing diverse microhabitats like boulders and vegetated edges. They usually congregate as a diverse school of fish that includes fish of all size groups, from juveniles, to sub-adults and adults. These fascinating fish are lovely to observe under water while snorkelling, exhibiting a non-skittish behaviour by welcoming observers into their aquatic realm. They manoeuvre in the water column by continuously moving their pectoral, pelvic and tail fins.
Distribution
Researchers from the National Research Foundation’s South African Institute of Aquatic Biodiversity (NRF-SAIAB) are in the process of describing the Goukou galaxias as a new species for science. This species is only known from short stretches of the upper Goukou River in the Western Cape Province. According to the lead researcher of this project, Professor Albert Chakona, Chief Scientist at NRF-SAIAB, this species of fish co-occurs with two other Cape endemics, the Cape kurper (Sandelia capensis) and the common galaxias (Galaxias sp. nov ‘nebula’). Through extensive surveys conducted as part of the NRF-SAIAB funded REFRESH project, researchers have conclusively determined that the Goukou galaxias species is endemic to the Goukou River. Surveys across numerous rivers in the Western and Eastern Cape provinces have shown no records of this species, indicating its exclusivity to the Goukou River. It is likely that this species could have once been distributed throughout the entire Goukou River system. Some sections of this river, particularly its lower stretches, have been severely impacted by pollution and the invasion of alien species. A recent survey conducted by collaborating organisations; NRF-SAIAB, Grootvadersbosch Conservancy Trust (GVBCT), and Gouritz Cluster Biosphere Reserve (GCBR) has confirmed that this species thrives in the upper Goukou. However, its long-term survival is at risk due to the possible migration of alien species from the lower Goukou, as there are no long-term barriers preventing their spread upstream.
Threats and conservation status
According to the IUCN Red List of Threatened Species assessment, the Goukou galaxias is categorised as Vulnerable, primarily because of its limited distribution. The vulnerability of its existence becomes evident when considering the potential threats it faces within its habitat such as the prevalence of alien invasive species. Dr Chakona and Dewidine Van der Cloff, SANBI Red List Scientist, outlined that the extensive spread of the Palmeit plant (Prionium serratum) in the Broomvlei wetland plays a crucial role by potentially acting as a barrier, hindering the upstream movement of these alien invasives. However, they also note that the urgency to implement effective conservation measures for this species remains crucial, as there are no natural barriers shielding it from alien invasive species. Ensuring the continued protection and preservation of its habitat is essential to safeguarding the future of this unique species, as these fish depend significantly on their environment for survival and reproduction.
Remarks
There is limited knowledge about this species’ life cycle, diet, and feeding behaviour. Thus, it is therefore crucial to explore these areas in depth for a better understanding of their nature and to enhance their conservation and protection from the various threats they are facing. Furthermore, additional surveys are needed to investigate their habitats, dietary preferences, and their reproductive habits.
Species Storage
Live colour pictures, voucher specimens and tissue samples of Galaxias sp. nov. goukou are available in National Fish Collection Facility and National Aquatics Biobank at the NRF-SAIAB. These photographs, specimens and tissues have been diligently catalogued, ensuring their preservation for future studies. Upon description, type specimens of this species will be deposited in other natural history museums as paratypes. Paratypes are specimens used along with the type specimen to define the scientific name assigned to a species.
Relatives to the Goukou galaxias
South Africa currently has only one valid species of Galaxias, G. zebratus, but the study conducted by Prof Chakona et al. (2013) has shown that there are more than 10 species that were included into this one species. These species have been assigned ‘nicknames’ to aid with communication, while they are being officially described. These lineages are: G. sp ‘nebula’, G. sp. ‘gouritz’, G. sp. ‘goukou’, G. sp. ‘heuningnes’, G. sp. ‘breede’, G. sp. ‘mollis’, G. sp. ‘riviersonderend’, G. sp. ‘verlorenvlei’, G. sp. ‘slender’, G. sp. ‘klein’, G. sp. ‘joubertina’. Interestingly, the G. sp ‘nebula’ co-occurs with most of these lineages as it is widely distributed across the Cape region, from the Bitou River system in the Eastern Cape to the Olifants-Doring river system on the west coast.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Osmeriformes
Family: Galaxiidae
Genus: Galaxias
Species: Galaxias sp. nov ‘goukou’
Top of Form
References
Chakona, A., Swartz, E.R. and Gouws, G., 2013. Evolutionary drivers of diversification and distribution of a southern temperate stream fish assemblage: testing the role of historical isolation and spatial range expansion. PLoS One, 8(8), p.e70953.
Chakona A, & Van Der Cloff D. 2016. Galaxias sp. nov ‘goukou’. The IUCN Red List of Threatened Species. http://speciesstatus.sanbi.org/assessment/last-assessment/131/ . Accessed 20 February 2024
