INTRODUCTION
The fish of the family Trachipteridae are characterized by long compressed ribbon or tape-shaped body, short head, and narrow mouth (Heemstra & Kannemeyer, Reference Heemstra, Kannemeyer, Smith and Heemstra1986). The pectoral fin is small, pelvic long and fan like in young composed of several rays, absent in adults. Anal fin absent. These fish also have a high dorsal fin that actually occupies the entire length of its back with origin well behind tip of snout. Eyes are large. The family comprises three genera—Trachipterus, Desmodema and Zu, altogether with 16 species (Nelson, Reference Nelson2006). Walters (Reference Walters1963) regards Zu as most generalized and Desmodema as most specialized of the three trachipterid genera. These two genera are closely related in the presence of dermal tubercles in large prejuveniles and tubercles and a cutaneous pore system in juveniles and adults.
Desmodema is distinguished from Trachipterus on the basis of nature of the caudal fin (parallel to body axis), the length of gastric caecum and the absence of sharp tipped mid-ventral tubercles (Walters & Fitch, Reference Walters and Fitch1960). In addition to this, in the species of Desmodema there are seven pterygophores before the first and second neural spines and in Zu and Trachipterus there is a single pterygophore before the first neural spine and nine between the first and second neural spines. Two species have been identified in the genus Desmodema—Desmodema polystictum (Ogilby, Reference Ogilby1897) and Desmodema lorum, Rosenblatt & Butler, Reference Rosenblatt and Butler1977. The caudal structure of D. polystictum is unique in Trachipteridae in that all of the caudal rays are borne on the terminal centrum and the hypural of the first ural centrum is rayless. Desmodema polystictum does not have scales; instead tubercles and pores are developed. Young ones of D. polystictum are silvery with profuse dark spotting (polka dotted) but the adults lack spots.
Froese & Pauly (Reference Froese and Pauly2010) state that Desmodema polystictum probably has a circumtropical distribution; it was reported from Japan, Taiwan (Shen, Reference Shen1993), Philippines, Australia, New Zealand (Paulin et al., Reference Paulin, Stewart, Roberts and McMillan1989); Western Pacific (Ogilby, Reference Ogilby1897) and 16°11′N to Namibia (Aguiar & Quéro, Reference Aguiar, Quéro, Query, Hureau, Karrer, Post and Saldanha1990); South Africa in the eastern Atlantic; Florida, USA (Moore et al., Reference Moore, Hartel Karsten, Craddock and Galbraith2003); Cuba (Robins & Ray, Reference Robins and Ray1986) in the western Atlantic and recently from depths of 500 m in the western Pacific (Mundy, Reference Mundy2005). Bauchot & Bianchi (Reference Bauchot and Bianchi1984) have reported the capture of a single specimen of D. polystictum at 72 m depth from the North Indian Ocean between 24001′N and 66032′E. The species has hitherto not been reported from the Indian waters and the present account is the first record of this species from these waters.
MATERIALS AND METHODS
A single specimen (107 cm total length and weight 480 g) of Desmodema polystictum (Ogilby, Reference Ogilby1897) was collected (Figure 1) from Tharuvaikulam landing centre (8°53′42″ N 78°09′60″E) north to Tuticorin on the south-east coast of India (Figure 2) on 16 September 2010 and identified based on the available literature (FAO, 1984) and FishBase (Froese & Pauly, Reference Froese and Pauly2010). The specimen was deposited in the National Marine Biodiversity Referral Museum at the Central Marine Fisheries Research Institute, Kochi (ref. no. GB.23.6.1.1). The fish was caught in a mechanized drift gill net (Paruvalai) boat, at a depth of 150–400 m while conducting ‘thangal fishing’ (stay-over fishing by large mesh sized gillnets) for 3–5 days. All counts and measurements were taken following Masuda et al. (Reference Masuda, Amaoka, Araga, Uyeno and Yoshino1984). The morphometric and meristic characters of the present specimen are given in Table 1.
Fig. 1. Map of India showing the location of Tuticorin, the place of collection of the present specimen.
Fig. 2. Desmodema polystictum, 107 cm total length, caught off Tuticorin south-east coast of India.
Table 1. Morphometric and meristic measurements of present specimen of Desmodema polystictum (Ogilby, Reference Ogilby1897) compared with the measurements given in FishBase (Froese & Pauly, Reference Froese and Pauly2010).
RESULTS
SYNONYMS
Desmodema polystictum (Ogilby, Reference Ogilby1897); Yabe in Amaoka et al., 1983:127, 202; Heemstra & Kannemeyer, 1984, Annals of the South African Museum 94: 15; Mundy, Reference Mundy2005, Bishop Museum Bulletins in Zoology 6: 237.
Trachypterus deltoideus Clark, 1938, Proceedings of the California Academy of Sciences 22: 180 (Rurutu Island, Austral Islands).
Trachypterus misakiensis, Tanaka, 1908, Journal of the College of Science, Imperial University 23: 52, pl. 4 (figure 2) (Misaki, Sagami Sea, Japan).
Trachypterus jacksoniensis polystictus Ogilby, 1898, Proceedings of the Linnean Society of New South Wales 23: 649 (off Newcastle, New South Wales, Australia).
Trachipterus woodi Smith, 1953, The sea fishes of southern Africa: 504, figure 264b (Xora River mouth, Transkei).
DESCRIPTION OF THE SPECIMEN
Body strongly compressed laterally, dorsal spines nil, soft rays 121; post-anal portion of body narrowing into a whip-like tail. Seven pterygophore before first neural spine and one or two pterygophore between first and second neural spines. First pterygophore closely applies to back of skull, no predorsal bones. Caudal fin well-developed, 4–10 unbranched rays parallel to axis of tail. All caudal rays borne on last ural centrum. No ventral caudal lobe. Fin rays with a lateral row of small spines, spines weak or absent on posterior pelvic rays, middle caudal rays and pectoral rays. Each dorsal ray anterior to elongated tail portion of body with a single laterally directed stout spine on either side of the base. Lateral line ends at caudal base, lateral-line scales with a pair of spines. Skin with cartilaginous tubercles and pierced by numerous pores which seems to be pores of the lateral line which is in agreement with Walters (Reference Walters1963). Teeth restricted to one to four in each pre-maxilla and two enlarged, recurved fangs on mandible, one on either side of symphysis. Rakers of upper limb with few teeth. Pseudobranch well developed.
DISCUSSION
The present specimen is identified as D. polystictum due to its short snout (smaller than eye diameter) and eight numbers of caudal rays (Table 1) whereas D. lorum has a longer snout (greater than eye diameter) and six numbers of caudal rays. Desmodema lorum appears to be restricted to the northern Pacific region, whereas D. polystictum is broadly distributed in the tropical Pacific and in the South African waters. The northern and southern most records of this species are in areas influenced by warm currents (Rosenblatt & Butler, Reference Rosenblatt and Butler1977). Desmodema lorum is mostly distributed in the cooler waters of the North Pacific. Desmodema polystictum distribution in the Atlantic rests on the records of Leapley (Reference Leapley1953) and Walters (Reference Walters1963) and also from the central and southern Atlantic. The morphometric and meristic measurements agree well with the characters given by Heemstra in FishBase (Froese & Pauly, Reference Froese and Pauly2010) and Ogilby (Reference Ogilby1897).
The present report is significant in the sense that even though D. polystictum is considered as circumtropical, a huge gap existed in the distribution of this species. The distribution range of this species until this record was made extended from the Pacific Ocean to Atlantic Ocean and Northern Indian Ocean. With the present report, the distribution range of this species now extends to the Indian waters but may be considered as rare occurrence only.
ACKNOWLEDGEMENTS
The authors wish to express their gratitude to the Director, Central Marine Fisheries Research Institute (CMFRI), Cochin for facilities and the Scientist in Charge, TRC of CMFRI, Tuticorin for encouragement. The authors are thankful to Professor Karsten E. Hurtle, of the Museum of Comparative Zoology, Harvard University, Massachusetts for providing materials and literature for identification of the specimen and Smt Rekha J. Nair, Scientist, CMFRI for help in collection of literature.
