Generalized Form of Barbs of the Barbus (=Labeobarbus) intermedius Complex in Lake Tana: Vectors of Morphological Variability at Different Stages of Postnatal Ontogenesis

Abstract—Fishes of the Barbus (=Labeobarbus) intermedius complex (Actinopterigii, Cyprinidae), known in Russian-language literature as Large African Barbs, are widely distributed in Africa water bodies. A special feature of the morphological diversity of this group of fish is the sympatric coexistence of morpho-ecological forms in local populations. The most famous example of such coexistence takes place in Lake Tana located in the north of Ethiopia, where, according to different authors, up to 15 morpho-ecological forms (morphotypes) live. The diagnostic features of the barbs of Lake Tana morphotypes are clearly manifested upon reaching a standard length (SL) of approximately 15 cm. With a shorter length, representatives of most morphotypes are indistinguishable from each other. This suggests that, in ontogenesis, the main vectors of morphological variability of the Tana Lake barbs may be different before and after individuals reach a length of 15 cm. The aim of this study was to test this assumption. The results obtained confirm that, in this population, the standard length (SL), equal to approximately 15 cm, delimits two stages of postnatal ontogenesis in the studied group of fish. In individuals with SL < 15 cm, the main vector of variability is a consequence of changes in morphological proportions as the individual grows. In individuals with SL > 15 cm, the main vector of variability is most likely associated with the trophic resource partitioning. The original approach used in the study is considered promising in analyzing the peculiarities of variability at different stages of ontogenesis not only in the studied group but also in other systematic groups.