PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 115(3):564-569. 2002. Plotosus fisadoha, a new species of marine catfish (Teleostei: Siluriformes: Plotosidae) from Madagascar Heok Hee Ng and John S. Sparks (HHN & JSS) Fish Division, Museum of Zoology, University of Michigan, 1109 Geddes Avenue, Michigan 48109-1079, U.S.A. Abstract. — A new species of plotosid catfish, Plotosus fisadoha, is described from the coastal waters of southeastern Madagascar. Plotosus fisadoha can be distinguished from congeners by the following unique combination of char-acters: head length 23.7-23.9 %SL; head width 13.7-15.2 %SL; head depth 11.5-11.8 %SL; body depth at dorsal-fin origin 13.1-13.3 %SL; pectoral-fin length 14.9-15.0 %SL; pelvic-fin length 9.7-9.8 %SL; snout length 39.0-39.2 %HL; interorbital distance 32.9-33.4 %HL; eye diameter 13.1-14.3 %HL; na-sal barbel length 40.7-44.0 %HL; maxillary barbel length 47.0-52.3 %HL; outer mandibular barbel length 47.0-47.7 %HL; 58-59 vertebrae; 10 caudal-fin rays; 164-171 total confluent median fin rays; and uniform brown colora-tion. The family Plotosidae (eel-tailed catfish-es) is a small assemblage of marine and freshwater catfishes found throughout the Indo-Pacific. Allen & Feinberg (1998) rec-ognized 31 species in 10 genera. The sys-tematics of Plotosidae are poorly under-stood, and there have been few revisionary studies (e.g., Gomon & Taylor 1982, Allen 1998), none encompassing the entire as-semblage. Plotosus is primarily marine and distributed throughout the Indo-Pacific. Plotosus is distinguished from other ploto-sid genera by the following unique combi-nation of characters (Gomon & Taylor 1982): a dendritic organ posterior to the anus, gill membranes separate and free from the isthmus, four pairs of barbels, lips without lobes or barbel-like extensions, tu-bular anterior nostril at or above the edge of the upper lip, and teeth on the premax-illa. Of the characters described above, only the presence of a dendritic organ is a syn-apomorphy of some plotosids, although it is not unique to Plotosus (present also in Paraplotosus, Cnidogtanis, Euristhiuus and Otoplotosus). Six species of Plotosus are currently considered valid (Gomon & Tay-lor 1982; Ferraris in Randall & Lim 2000), viz. Plotosus abbreviatus Boulenger 1895, P. canius Hamilton 1822, P. limbatus Va-lenciennes, in Cuvier & Valenciennes 1840, P. lineatus (Thunberg 1787), P. nkunga Gomon & Taylor 1982, and P. papuensis Weber 1910. While conducting a survey of the fresh and brackish water fishes of Madagascar, the second author obtained specimens of Plotosus from the southeastern coast of the island that are morphologically distinct from any previously described species. The description of this material forms the basis of this contribution. Methods Measurements were made with dial cal-ipers and data recorded to 0.1 mm. Counts and measurements were made on the left side of the specimens whenever possible. Vertebral and median fin-ray counts were taken from radiographs. In tables and text, subunits of the head are presented as pro-portions of head length (%HL). whereas head length and measurements of body
BioStor
