New data on the clupeoids of lakes Mai-Ndombe and Tumba, western Democratic Republic of the Congo, using an integrated approach combining morphology and barcoding

Abstract

Morphological and molecular comparisons of clupeoid fishes in lakes Tumba and Mai-Ndombe in the Congo Basin revealed that a large-sized form of a common species in Lake Mai-Ndombe had not been distinguished from the small-sized endemic Mai-Ndombe dwarf sprat Nannothrissa stewarti Poll & Roberts, 1976 in ecological studies. The large-sized form differs from the Mai-Ndombe dwarf sprat in several morphological characters and resembles the smalltoothed pellonula Pellonula leonensis Boulenger, 1916, but in barcoding analysis appears more closely related to the bluntnosed sawtooth pellonuline Potamothrissa obtusirostris (Boulenger, 1909). This large-sized form is probably a species new to science but will remain undescribed for now, and is here referred to as Pellonulinae sp. BIG. A slender clupeoid, also from Lake Mai-Ndombe, has recently been referred to as the Lake Tumba dwarf sprat Nannothrissa parva (Regan, 1917), which would be the first record of this species from that lake. Specimens of a slender clupeoid collected from Lake Mai-Ndombe for this study were identified as the losera fangtooth pellonuline Odaxothrissa losera Boulenger, 1899. This is the first confirmed occurrence of this species in Lake Mai-Ndombe, whereas the presence of N. parva could not be confirmed. The phylogenetic analysis strongly supports the genus Nannothrissa as currently delimited, here barcoded for the first time, but also confirms the previously reported mismatch between morphological classification and molecular data in this group. We further note that the Mai-Ndombe dwarf sprat attains a larger size than the maximum size noted in the original description in 1976, and it is suggested that an intense beach-seine fishery that utilises mosquito nets might have led to a population decline followed by decreased intraspecific competition, enhancing individual growth. For the same reason, Pellonulinae sp. BIG might have been less common previously and so remained undetected until now.