Indian Journal of Marine Sciences Vol. 38(2), June 2009, pp. 166-169 Redescription of Dicrolene nigricaudis (Alcock, 1899) a rare species of deep sea cusk eel (Ophidiiformes; Ophidiidae) from Indian EEZ Sherine Sonia Cubelio, Jinson Joseph, S. Venu, A.V. Deepu & B. Madhusoodana Kurup School of Industrial Fisheries, Cochin University of Science and Technology, Fine Arts Avenue, Cochin-682 016, Kerala India. [E.mail: [email protected]] Received 11 August 2008; revised 31 december 2008 Dicrolene nigricaudis (Alcock, 1899), a rare species of deep sea cusk eel described from Andaman Sea and Arabian Sea in 1899 is redescribed and compared with its closely related species, D. tristis in terms of meristics and morphometrics in order to establish its individual taxonomic identity. The specimens were collected during the fishery survey cruises of FOR V Sagar Sampada along the continental slope of Indian EEZ. D. nigricaudis is characterized by two median and a pair of basibranchial tooth patches and lower elongated free rays of pectoral fin. The paper highlights the taxonomic characters useful for species identification. [Keywords : fish, cruise, continental slope, demersal, pelvic, gill rakers] Introduction meristic characters 6, but due to insufficient The first authentic record of the deep-sea fishes knowledge of the intraspecific variation the key is from India was made with the help of fishes collected difficult to use 4. According to the prevailing by R.I.M.S Investigator in the book "Indian deep sea classification, four species viz, D. nigricaudis, D. fishes in the Indian museum” 1. Investigation on the tristis, D. vaillanti and D. longimana are pooled into deep sea fishes of India EEZ were mainly carried out one group where it shares a common taxonomic by Fisheriery Survey of India concentrating mostly in character of presence of two median basi branchial the continental shelf region. Data regarding the tooth patches. Further, it has been remarked that Indian deep sea fish fauna is scarce and only available various collections hold much untreated specimens information is that generated from the fishing and this genus needs a complete revision 4. D. vaillanti cruises of FOR V Sagar Sampada as part of its stock is considered to be a synonym of D. intronigra 1,2 . assessment programme of deep sea fin fishes. Recent Many authors have reported the taxonomic problems research cruises of FOR V Sagar Sampada have among different species of Dicrolene where the elucidated many little known deep sea fishes of the correct taxonomic identity of this genus is still order Ophidiiformes, which have not received much questionable 3,4,6 . Hence an attempt is made to attention hitherto. redescribe this deep sea fish comparing its Ophidiids are predominant member of deep sea morphometries and meristics with closely related demersal fishes from the continental slope to abyssal species viz, D. tristis. plain 2,3,4 . The earlier synopsis of Ophidiiformes fishes in India reported 15 genera of the family Materials and Methods Ophidiidae 1. The first catalogue of Ophidiiformes During cruise no: 250 of FOR V Sagar Sampada, focused at the genus level, and species classifications three specimens of D. nigricaudis were collected were not complete 5. Subsequent catalogue published using HSDT (High Speed Demersal Trawl) net from included all ophidiiformes fishes of the world which station number 13 (12° 55.3" N and 74° 07.7" E) at a describes 48 genera and 218 species of deep sea fishes depth of 740m on 8-11-2006 (Fig. 1). Specimens were under the family Ophidiidae 4. Genus Dicrolene deposited in Fish Museum of School of Industrial Goode & Bean, 1883 has 15 recognized species Fisheries, Cochin University of Science and under the subfamily Neobythitinae 4. A tentative key Technology, India. Morphometric measurements were to Dicrolene spp. was published mainly based on taken to the nearest mm using a dialed vernier CUBELIO et al REDESCRIPTION OF DICROLENE NIGRICAUDIS FROM INDIAN EEZ 167 also counted . Measurements of D. tristis were studied for comparison. Results Systematics Order OPHIDIIFORMES Cohen & Nielsen, 1978 Suborder OPHIDIOIDEI Cohen & Nielsen, 1978 Family OPHIDIIDAE Rafinesque, 1810 Subfamily NEOBYTHITINAE Radcliffe, 1913 Genus Dicrolene Goode & Bean, 1883 Dicrolene nigricaudis (Alcock, 1899) (Fig. 2, 3) Type material; Holotype 203.2mm (sex not mentioned 2) Andaman Sea, 188-220 fathoms, July 1891 Dicrolene nigricaudis Alcock, 1899: 87, p1.4.Nielsen & Cohen, 1999. Comparative material examined: Fig 1—Collection site of Dicrolene nigricaudis (Ο) from the Dicrolene tristis Smith and Radcliffe, 1913: 145, EEZ of India p1.8; Nielsen & Cohen, 1999; Lee et al, 2005 Material examined: SIF 2501, 2502, 2503; 199.44 mm SL, 199.48 mm SL; 303.20 mm SL: Off Mangalore, SW coast of India, 12° 55'3"N and 74° 07'7" E; HSDT net; 740m; Nov 11,2006. Fig 2— Lateral view of Dicrolene nigricaudis (Scale indicate 1 cm) Description: Meristics: Dorsal fin rays: 101; anal fin rays: 84; pelvic fin rays:2; pectoral fin rays:24; lower free rays of pectoral fins:6 ; caudal fin rays:9; total vertebrae:63 ; precaudal vertebtrae: 16-18. Morphometrics in SL (%): Head length: 25.7; predorsal length: 32.7; preanal length: 51.8; pectoral fin length: 39.5; pelvic fin length: 11.6; depth at first dorsal base: 22.3; anal fin base: 57.4. Morphometrics in HL (%) Eye length: 20.7; preorbital length: 20.1 Snout blunt; eye large; eye length almost equal to snout length and preorbital length; mouth large and terminal; upper jaw ends below posterior margin of eye. Premaxilla with two palatine and a vomerine tooth patches; opercular spine strong and straight. 3 short Fig 3—Basibranchial tooth patch of Dicrolene nigricaudis spines at hind margin of preopercle; 2 median and 2 (199.48 mm SL) basibranchial tooth patches, upper more elongated than caliper 7. Body proportions were expressed in lower (Fig. 3); branchiostegal rays 9; 2 pseudobranchial terms of standard length (SL: length from snout tip filaments; total gill rakers 15 with 9-10 developed rakers to the base of caudal fin) and head length on anterior gill arch. (HL: length of snout tip to the posterior margin of Body elongated; colour in formalin pale brownish; opercle).Vertebrae and fin rays of the fishes were posterior third of caudal, including the posterior parts 168 INDIAN J MAR SCI. VOL.38 No. 2, JUNE 2009 of dorsal and anal fins, is black; no blotches and spots Table 1— Meristic counts and proportional measurements of on body; body depth and head length are more or less D. nigricaudis and D. tristis. equal, head depth 1.3 times that of head length, small Morphometric cycloid scales covered; preanal length about twice of measurements D.nigricaudis D. tristis head length; pelvic fin placed below preopercle; lower (present specimen) 5-6 rays of pectoral fin free and longer; pectoral fin length 3.4 times that of pelvic fin length, dorsal fin Standard length (mm) 224.73 183.15 length 1.2 times that of anal fin length, dorsal fin and (% ofSL) anal fin joined with caudal fin; each pelvic fin with 2 Body depth 21.6 - separate rays. Precaudal vertebrae are 27 % of the Head depth 19.1 - total vertebrae. Depth at first anal base 18.2 - Depth at first dorsal base 22.3 15.9-16.8 Discussion Predorsal length 32.7 22.4-23.8 Original description of D. nigricaudis was from Preanal length 51.8 38-38.3 Indian Ocean and was very brief. However, available Dorsal fin length 72.4 73.5-76.4 data on the species has been reproduced in FAO Pectoral fin length 39.5 19.1-22.2 species identification sheets for Ophidiiform Fishes of Pelvic fin length 11.6 6.3-6.6 the world 4, where characters used to identify different Anal fin length 57.4 58.3-61.5 species were found to be overlapping. For instance, Head length (HL) 25.7 17.7-18.2 species viz, D. longimana, D. nigricaudis, D. tristis, (%HL) shares the similar character of two median and two Postorbital length 65 - basibranchial tooth patches 4. Main differences among Preorbital length 20.1 21.9-24.8 species of this genus are the numbers of median Eye length 20.7 24-29.1 basibranchial tooth patch and its comparative Depth at eye 54.3 - location 3,4,6 . However, it has been suggested that the Upper jaw length 59.5 - genus needs a thorough revision to assign specific MERISTIC COUNTS characters of taxonomic importance 4. In the present Branchiostegal rays 9 - Gill rakers 15 - study, a comparison of the morphometric counts of Developed gill rakers 10 11-14 D. nigricaudis and D. tristis 3 is made to differentiate Dorsal fin rays 101 98-101 between the closely related species. Meristics and Pectoral fin rays 24 27-33 proportional measurements of D. nigricaudis and D. Pelvic fin rays 2 2 tristis are shown in Table 1. D. nigricaudis resembles Anal fin rays 84 78-85 D. tristis in many morphomeristic characters like Caudal fin rays 9 6 dorsal fin base, anal fin base, preorbital length, dorsal Precaudal vertebra 17 15-16 fin rays, pelvic fin rays, anal fin rays, precaudal and Total vertebra 63 62 caudal vertebrae counts. A thorough comparative study on morphometrics of both D. nigricaudis and D. (Source) D. tristis: Lee et al (2005) tristis has given a concrete base to distinguish of Dicrolene can also be used to identify the species between the species. Furthermore, the taxonomic under study. As suggested in the earlier studies, the identity of D. nigricaudis is confirmed due to the genus did not have a complete revision what may possession of many distinct characters such as depth be due to similar characters among species 3.