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 <i>Nannothrissa stewarti</i> Poll &amp; 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 <i>Pellonula leonensis</i> Boulenger, 1916, but in barcoding analysis appears more closely related to the bluntnosed sawtooth pellonuline <i>Potamothrissa obtusirostris</i> (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 <i>Nannothrissa parva</i> (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 <i>Odaxothrissa losera</i> Boulenger, 1899. This is the first confirmed occurrence of this species in Lake Mai-Ndombe, whereas the presence of <i>N. parva</i> could not be confirmed. The phylogenetic analysis strongly supports the genus <i>Nannothrissa</i> 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.