Glossogobius, a species-rich gobiid genus with 42 recognized species distributed in the Indo-West Pacific, lacks a comprehensive phylogenetic analysis. The highest diversity of the genus occurs in the tropical West Pacific, highlighting this region as a centre of endemism. In contrast, the Indian Ocean has lower diversity (nine species). This study offers the first thorough description of Glossogobius diversity in the south-western Indian Ocean through integrative analyses. Our findings reveal nine lineages, five of which are newly identified, including a new species, Glossogobius hanisii sp. nov., described from southern Africa and Madagascar. Seven species/lineages, along with G. kokius from Mauritius and G. tenuiformis, are endemic to the south-western Indian Ocean. With 65% of Indian Ocean Glossogobius species/lineages being endemic to the south-western region, it is identified as a hotspot of endemism. The genetic structuring of these lineages along the east coast of southern Africa appears to be shaped by an interplay between life history, oceanographic conditions, and adaptations to marine biogeographic regions. Additionally, our findings highlight Madagascar’s central role in Glossogobius diversification and evolution of unique gobies, provide a framework for a comprehensive revision of Glossogobius in the region, and facilitate the identification of conservation units and the formulation of management measures.

A southwestern Indian Ocean (SWIO) percoid fish Serranus knysnaensis Gilchrist, 1904, was long synonymised with the comber, Serranus cabrilla (Linnaeus, 1758), from the eastern Atlantic Ocean, Mediterranean and Black Sea. However, when the species was brought out of synonymy by Heemstra & Heemstra (2004), reasons for this decision were not given. This study aims to revalidate the present taxonomic status of S. knysnaensis using morphological and molecular assessments. The two species are distinguished by the number of circumpeduncular scales (26–34 in S. knysnaensis versus 34–38 in S. cabrilla) and total gill rakers (18–22 versus 22–24). Serranus knysnaensis is also distinct from S. novemcinctus Kner, 1864, the other SWIO species of Serranus, based on total gill raker counts (18–22 versus 31–35). Genetic analysis of mitochondrial DNA barcode (COI) sequences for 17 Serranus species revealed three closely-related monophyletic clusters corresponding to S. cabrilla, S. novemcinctus and S. knysnaensis that were supported (P <0.001) by species delimitation methods. Even though the genetic distances among the three species were the lowest in the genus (1.60−1.99%), these species may be ecomorphs or lineages that have only recently diverged from each other. These three species also have allopatric distributions and our morphological and molecular data thus confirm that S. knysnaensis is a valid species.

The Zambezi grunter, Parauchenoglanis ngamensis, is currently distributed across four (sub)basins in southern and south-central Africa, namely the Okavango, upper Zambezi, Kwanza, and Kasai. The present study used a combination of molecular (barcoding), colour pattern, and other morphological data to explore the possible existence of hidden species diversity within this species. Based on the available samples, analyses of molecular data uncovered seven well-supported (.96–1.00 Bayesian posterior probabilities) candidate species, with 1.6%−8.5% genetic divergence between them. These, in addition to two more candidate species without genetic data, exhibited a combination of consistent colour pattern and other morphological differences that supported their distinction. The present study redescribes P. ngamensis, which is confined to the Okavango and upper Zambezi (sub)basins, and describes eight new species: two from the Kwanza Basin and six from the Kasai sub-basin. The fact that some of the species occur allopatrically, whereas others are sympatric and even syntopic indicates the complex palaeogeographical history of these basins. In addition, the high species diversity discovered in the Kasai sub-basin seems to be related to its highly peculiar hydrography. Accurate delimitation of species boundaries and mapping of their distribution is crucial for conservation assessments and guiding their protection.

The taxonomic status of the widely distributed Indo-Pacific undulated moray eel, Gymnothorax undulatus, is revised using morphological and genetics features. Ninety-seven specimens previously identified as G. undulatus were examined and their mitochondrial COI and 16S rRNA genes were analysed. The multivariate analysis of eight morphometric characters resulted in separation with little to no overlap among some geographic regions. These groupings explained more than 90% of the total variation, with 86.6% overall classification. Two color morphs were identified, and the South African population was described as new species, Gymnothorax elaineheemstrae n. sp., distinct from G. undulatus in having mottled and faintly reticulated color pattern, 134–136 total vertebrae and further confirmed by the genetic analysis of COI and 16S rRNA with > 0.1 genetic distance. The morphological and genetics results indicate that G. undulatus, previously treated as a single species, consists of more than one species.

The oriental armored gurnard, Scalicus orientalis (Fowler), a benthic species in the family Peristediidae, is redescribed based on a specimen collected in 2023 from off the coast of Mozambique during an ecosystem survey by the R/V Dr. Fridtjof Nansen, alongside four comparative specimens housed in the NRF-SAIAB National Fish Collection. This study is part of a post-survey taxonomic initiative under the EAF-Nansen Programme, aimed at strengthening taxonomic capacity in the East African region and advancing knowledge of its marine fish biodiversity. Detailed morphological analyses, including updated meristic and morphometric data, are presented with illustrations of both fresh and preserved coloration. DNA barcoding of the mitochondrial COI gene was used to support morphological identification, and species boundaries within the genus Scalicus were further evaluated using three molecular species delimitation methods: assemble species by automatic partitioning (ASAP), automatic barcode gap discovery (ABGD), and Bayesian implementation of the Poisson tree process (PTP). The results confirm the identification of the Mozambican specimen as S. orientalis, representing the first report of this species from the East African coast and the second record from the southwestern Indian Ocean. A revised key to the species of Scalicus is also provided.