Comparative morphology of scales of four teleost fishes from Sudan and Yemen LAITH A. JAWAD Upper Hutt, Wellington, New Zealand (Accepted 2 March 2005) Abstract The scale morphology of four teleost fishes, Barbus arabicus, B. exolatus, Labeo niloticus (Cyprinidae), and Lates niloticus (Centropomidae), was studied using both light and scanning electron microscopy. The considerable variation in scale shape on different parts of the body makes it difficult to nominate a typical scale for particular species to be used in taxonomic studies. However, some character states of the inter-radial denticles, cteni, and the focus area appear to be good taxonomic criteria. Keywords: Barbus, cteni, Labeo, Lates, morphology, scales, SEM, Sudan, Yemen Introduction The use of scale morphology and squamation (lepidology) in fish classification can be traced back to the time of Agassiz (1834), who apparently was the first to use fish scales for taxonomy and divided fishes into four groups according to the structure of their scales: Placoidei, Ganoidei, Ctenoidei, and Cycloidei. The importance of scale morphology in systematic studies increased dramatically during the late 19th century and the first half of the 20th century, with great advancements in the field of light microscopy (Williamson 1851; Baudelot 1873; Timms 1905; Cockerell 1910, 1913, 1914, 1915; Chu 1935; Lagler 1947; Kobayasi 1951, 1952, 1953, 1955; McCully 1961; and others). The value of scale morphology used in classification was enhanced with the introduction and development of scanning electron microscopy (SEM) (DeLamater and Courtenay 1973, 1974; Hughes 1981; Roberts 1993; Lippitsch 1990, 1992, 1993). However, some problems in the use of scale morphology due to environmental factors, and variation in shape, size and structures according to age and position on the body have been reported (Lippitsch 1990; Pou and Gallego 1990). A comparative morphological study of the scales of four freshwater fishes from the Nile River at Dongola, Sudan and stream water at Eib province, Republic of Yemen was Correspondence: Laith A. Jawad, 15 Birkinshaw Grove, Riverstone Terraces, Upper Hutt, , Wellington, New Zealand. Email: zainab@clear.net.nz Published 19 July 2005. Journal of Natural History, 2005; 39(28): 2643–2660 ISSN 0022-2933 print/ISSN 1464-5262 online # 2005 Taylor & Francis Group Ltd DOI: 10.1080/00222930500102801