NEW RECORDS OF MARINE FISHES FROM THE CORAL REEFS AND DEEP WATERS OF GULF OF MANNAR, INDIA

Background. The coral reefs and deep water ecosystems of Gulf of Mannar support diverse assemblages of marine fishes vulnerable to indiscriminate mechanized fishing. However, lack of comprehensive information on the fish diversity of these ecosystems is aggravated by the habitat complexity of the fishing grounds, inadequate faunistic surveys and insufficient taxonomic expertise. In view of this, the present paper aims to document rare fishes and supplement the existing species inventory from this region. Materials and methods. Sampling surveys included 23 hauls on-board commercial single-day otter trawlers operating bottom trawls at 15–100 m depths, and mid-water trawls at 100–153 m depths in the Gulf of Mannar. In addition, by-catch landings of commercial trawlers were surveyed at Tuticorin fishing harbour. Specimens were subjected to morphometric and meristic examination and deposited at the Central Marine Fisheries Research Institute, Kochi. Results. The presently reported survey of rare fishes revealed one elasmobranch, Hypogaleus hyugaensis (Miyosi, 1939). In addition, 12 species of teleosts belonging to four orders, 10 families, and 11 genera were identified as Uropterygius micropterus (Bleeker, 1852); Dendrochirus bellus (Jordan et Hubbs, 1925); Snyderina guentheri (Boulenger, 1889); Acropoma japonicum Günther, 1859; Gymnocranius elongatus Senta, 1973; Pomacentrus similis Allen, 1991; Pristotis cyanostigma Rüppell, 1838; Leptojulis cyanopleura (Bleeker, 1853); Naso annulatus (Quoy et Gaimard, 1825); Naso thynnoides (Cuvier, 1829); Pseudalutarius nasicornis (Temminck et Schlegel, 1850); and Lagocephalus suezensis Clark et Gohar, 1953. The present paper provides descriptions of each species supplemented with meristic counts and morphometric measurements. An identification key to these species is provided. Conclusion. Hypogaleus hyugaensis, U. micropterus, D. bellus, P. cyanostigma, N. thynnoides, P. nasicornis, and L. suezensis represent the first records in Indian waters. Additionally, G. elongatus, P. similis, and N. annulatus represent the first records off the Indian mainland, and S. guentheri, A. japonicum, and L. cyanopleura represent the first records off the East coast of India. Among these, D. bellus, S. guentheri, and P. cyanostigma represent the first records outside their known zoogeographical ranges. Patchy zoogeographical distribution and extension of known geographical ranges are attributed to recurrence of vicariance events in the geological past.


INTRODUCTION
The Gulf of Mannar with an area of 10 500 km 2 is situated off the southeast coast of India and comprises 21 small islands surrounded by fringing coral reefs (Venkataraman et al. 2004). The sub-tidal habitats comprise live coral cover, coral boulders with encrusting algal beds at 10-50 m depths (Prakash and Kumar 2016). Thomas (1970) described new sponges associated with deep water corals of the genus Pachyseris up to 180 m depth indicating the existence of deep water reefs in this region. This ecosystem reportedly supports > 900 reef-associated finfish species, which are being gradually removed by large scale mechanized fishing (Yogesh Kumar et al. 2013). This region is also prone to tremendous anthropogenic pressure owing to large scale industrial and shipping activities, which are potentially hazardous to the fragile coral reefs and sea-grass habitats (Kathal 2005).
Therefore, in order to assess the diversity of demersal fishes in the Gulf of Mannar, trawling surveys onboard commercial trawlers were undertaken off the V.O. Chidambaranar Port, Tuticorin. These surveys revealed thirteen new records of rare fishes in the Indian waters, and supplement the existing information pertaining to the finfish diversity in this region.

MATERIALS AND METHODS
The area of the presently reported study encompasses the trawling grounds in the Gulf of Mannar, located off the south-eastern coast of India ( Fig. 1) from 15 through 153 m depth. The bathymetry of the study area (between latitudes 8°27′54′′N and 8°52′43′′N and longitudes 78°12′33′′E and 78°32′38′′E) is characterized by gentle gradient from the shoreline to 20 m depth, followed by slightly steep gradient between 20 m and 50 m depth contours, and very steep gradient between 50 m and 500 m depth contours (Anonymous 2010). Sampling surveys were carried on-board commercial single-day otter trawlers operating bottom trawls at 15-100 m depths, and mid-water trawls at 100-153 m depths in the Gulf of Mannar during July 2012 to March 2013 with a total effort of 35 man hours. Altogether, 23 bottom trawl hauls were examined. Rare fishes hauled up by trawl nets were collected, photographed, temporarily preserved on ice, and taken to the laboratory for detailed examination. Additionally, rare fishes were also collected from by-catch of commercial trawlers at Tuticorin fisheries harbour.
At the laboratory, taxonomic identification was carried out following FAO Species Identification Sheets (Carpenter and Allen 1989, Compagno and Niem 1998, Böhlke et al. 1999, Poss 1999, Allen 2001, Hutchins 2001, Matsuura 2001, Randall 2001a, Westneat 2001). Detailed morphometric and meristic studies of each species were carried out following the specifications provided by published literature relevant to each taxon. Morphometric measurements of Hypogaleus hyugaensis (Miyosi, 1939) and Uropterygius micropterus (Bleeker, 1852) are expressed as percentages of Total Length, whereas those of the other eleven species are expressed as percentages of Standard Length.
Reference voucher samples were deposited in the Marine Biodiversity Museum of Central Marine Fisheries Research Institute, Kochi (a designated national repository), and accession numbers to specimens are provided in the Results section.
The presently reported study was carried out on board commercial trawlers in accordance with the Indian national regulations and did not require any special permit.

Hypogaleus hyugaensis
The identification of the presently reported specimen following the dichotomous key to species of the family Triakidae (see Fischer and Bianchi 1984) revealed that in the first step, this specimen differed from Scylliogaleus quecketti Boulenger, 1902 in having rudimentary nasal flaps widely spaced from each other (nasal flaps large and meet each other in the latter species). Moreover, it lacks nasoral grooves (present in the latter species).
According to the second step, this specimen possesses rudimentary anterior nasal flap, a prominent ventral caudal lobe, its D 2 is half the size of D 1 . On the other hand, sharks of the genera Iago and Mustelus possess short anterior nasal flap, short ventral caudal lobe and D 2 almost as large as D 1 . In the third step, this specimen keys out as Hypogaleus hyugaensis owing to an angular mouth, D 2 larger than A, and terminal lobe of caudal fin one-thirds in length of total caudal fin dorsal margin length. The other species in the third step, Galeorhinus galeus (Linnaeus, 1758) possesses an arcuate mouth, equally large D 2 and A, and a comparatively longer terminal lobe of caudal fin.  (McCosker and Smith 1997). This genus comprises 20 valid species, out of which 16 are distributed in the Indo-western Pacific region, two in eastern Pacific region, and one each in eastern Atlantic and western Atlantic regions (Smith 2012). Among these, three species namely Uropterygius concolor; Uropterygius macrocephalus (Bleeker, 1864); and Uropterygius marmoratus (Lacepède, 1803) are known from the Indian waters (Rao et al. 2000). ( (Bleeker, 1852): Heemstra 1986: 175, fig. 41.31. Böhlke andMcCosker 2001: 76 (key). Loh et al. 2008: 140, fig. 1G. Material. GB.4.9.12.10,(1,165.00 mm TL), by-catch landed at Tuticorin fisheries jetty, 10 July 2012. Diagnosis. Body eel-like, slender, pale grey coloured, overlaid laterally and dorsally with a reticulation of fine, brown, worm-like lines. Body (head and trunk) slightly more than 2.0 times, tail slightly less than 2.0 times in total length. Head pores 13 (one branchial, two supraorbital, four infra-orbital, six mandibular). Posterior nostril not contiguous with supra-orbital pore. Teeth pointed, biserial. Single lateral-line pore above and before gill opening. Dorsal and anal fins restricted to tail tip. Description. Body eel-like, slender (BD 3.72% of TL, BD at gill opening 2.02% of TL, BD at anus 2.74% of TL, BW 2.46% of TL), pale to grey coloured, overlaid laterally and dorsally with a reticulation of fine, brown, worm-like lines. Anus positioned near mid-length, body (snout to anus distance) 47.43% of TL, tail (anus to posterior caudal tip distance) 52.57% of TL. Head short (HL 12.79% of TL). Head pores 13 (one branchial, two supra-orbital, four infra-orbital, six mandibular). Snout extremely short (SnL 1.59% of TL), snout tip to mouth corner 4.34% of TL. Mouth terminal, small (UJL 3.55% of TL, LJL 4.32% of TL). Jaw teeth pointed, biserial, inner series long caniniform; vomerine teeth short caniniform. Posterior nostril located over front of eye, not contiguous with supra-orbital pore. Eye small (ED 0.67% of TL), IOW 0.92% of TL, eye to mouth corner distance 1.30% of TL. Single lateral-line pore above and before gill opening. Gill opening small (1.18% of TL). D and A restricted to tail tip, embedded in skin. No trace of fin on mid-ventral surface just behind anus. C extremely short (longest middle ray 0.15% of TL). Distribution. Previously known from the east coast of Africa to Japan, Australia, and the central Pacific regions (Loh et al. 2008). This specimen represents the first record in the Indian waters. Remarks. The identification of the presently described specimen following the dichotomous key to subfamilies of family Muraenidae (see Böhlke et al. 1999) revealed that this specimen keyed out to subfamily Uropterygiinae owing to the restriction of the dorsal and anal fins to caudal tip. Subsequent identification following the key to species of subfamily Uropterygiinae revealed that in the first step, the specimen differed from Channomuraena vittata (Richardson, 1845) in having subequal jaws, long snout, and eye above middle of jaws. In the second step, this specimen differed from the genus Anarchias in lacking pore abutting posterior nostril. In the third step, it differed from the genus Scuticaria in having subequal head-trunk and tail due to middle position of anus, a character shared by all Uropterygius species. In the fourth step, it differed from Uropterygius fasciolatus (Regan, 1909); Uropterygius kamar McCosker et Randall, 1977;Uropterygius xanthopterus Bleeker, 1859; in having one pore anterior to gill opening. In the fifth step, this specimen differed from Uropterygius nagoensis Hatooka, 1984 in having one pore anterior to gill opening (the latter species may or may not have pore). In the sixth step, it differed from Uropterygius concolor Rüppell, 1838 andUropterygius inornatus Gosline, 1958 (plain colour) in having markings on body. The subsequent three steps distinguished this specimen from Uropterygius polyspilus (Regan, 1909); U. marmoratus; and Uropterygius fuscoguttatus Schultz, 1953 (all three with different spotted patterns) in having vermiculate markings on body. In the tenth step, the specimen differed from Uropterygius supraforatus (Regan, 1909) in having biserial jaw teeth and vermiculate markings. In the eleventh step, the specimen keyed out as U. micropterus owing to brown vermiculate pattern, posterior nostril above front of eye, and SnL : ED ratio of 2 : 1. The other two species in this step, U. macrocephalus possesses posterior nostril placed above the middle or posterior part of the eye, and SnL : ED ratio greater than 2 : 1. Remarks. Dendrochirus is distinguished from closely related genera in having elongated dorsal fin with membrane deeply incised between spines, P with branched upper rays, fin membrane between these slightly incised, A with III spines and 5 soft rays (Poss 1999). This genus comprises six valid species, all of which are distributed in the Indo-Pacific regions (Poss 1999, Matsunuma andMotomura 2013). Among these, two species namely Dendrochirus brachypterus (Cuvier, 1829) and Dendrochirus zebra (Cuvier, 1829) are known from the Indian waters (Rao et al. 2000). Diagnosis. Dorsal fin spines 13, dorsal fin rays 10; anal fin spines 3, anal fin rays 5, pectoral fin rays 17, pelvic fin spine 1, pelvic fin rays 5. Total GR 20. Vertical scale rows about 36. SnL 5.65%-8.45% of SL; HL 26.72%-41.31% of SL; BD 38.77%-40.85% of SL. Body with broad red vertical bars on a pale background; P bright red with six broad black bands, lower P rays with alternating rows of light yellow and black spots. Description. Dorsal fin spines 13, dorsal fin rays 10; anal fin spines 3, anal fin rays 5; pectoral fin rays 17; pelvic fin spine 1, pelvic fin rays 5. Total GR 20. Body deep (BD 38.77%-40.85% of SL), moderately slender (BW 22.00%-25.70% of SL), light reddish coloured with six broad, slightly darker bands. Head long (HL 26.72%-41.31% of SL), robust (HW 22.49%-27.06% of SL), with short snout (SnL 5.65%-8.45% of SL). Mouth large (UJL 16.81%-20.52% of SL, maxillary depth 5.07%-8.26% of SL), gape slightly oblique. Jaw teeth slender, conical, vomerine tooth patch V-shaped. Anterior nostril with short tentacle, another on ventral margin of lacrimal spine. Eyes large (ED 12.07%-14.18 % of SL); IOW narrow (5.26%-6.75% of SL), with two longitudinal ridges. Nasal spine two-tipped; pre-ocular spine with four tips; supra-ocular spine with three points; post-ocular spine with nine tips; tympanic spine with two tips; coronal spine with three tips; parietal spine with wide base and one tip; nuchal spine with one tip; sphenotic spine with nine tips; pterotic spine with ten tips; lower post-temporal with one tip; supra-cleithral base serrated, one low spine at posterior edge; pre-opercular spines 3, uppermost spine largest and marked with distinct black blotch; sub-orbital ridge serrated in two distinct groups; lateral lacrimal ridge with 2 spines; posterior lacrimal spine directed posterolaterally. Scales large ctenoid, arranged in 36 vertical scale rows. Lateral line complete, sloping downwards; scales above lateral line 5. D origin above operculum (PDL 20.93%-27.64% of SL). D long (longest D spine 26.52%-29.55% of SL), membranes between spines deeply incised, (longest D ray 24.70%-26.69% of SL). P long (longest P ray 46.98%-49.41% of SL), reaching posterior end of A fin. P upper rays bright red with six broad black bands, lower rays bright red with alternating rows of light yellow and black spots. V origin slightly anterior to pectoral insertion (PVL 32.90%-35.27% of SL). V long (V spine 16.67%-20.59% of SL, longest V ray (30.31%-32.94% of SL), reaching beyond A origin. A origin under 12th dorsal spine (PAL 61.83%-69.96% of SL). A short (longest A spine 13.64%-20.97% of SL; longest A ray 27.28%-28.82% of SL). Caudal peduncle short (CPL 9.68%-12.73% of SL), deep (CPD 10.66%-12.35% of SL). C long (28.79%-31.57% of SL). D, A, V, and C bright red with alternating rows of small-sized light yellow and black spots. Distribution. Previously known from New Caledonia, Taiwan (Poss 1999) and Japan (Matsunuma and Motomura 2013). These specimens represent the first record in the Indian waters, and the first outside the known geographical range. Remarks. The identification of the presently described specimens following the dichotomous key to species of Family Scorpaenidae (Poss 1999) revealed that these specimens with skin at gill openings connected to each other, immobile lacrimal bone, single spine at end of weak opercular ridge, elongated D fin with deeply incised membranes between spines and an elongated pectoral fin keyed out as Subfamily Pteroinae. Subsequently, these specimens differed from the genus Pterois in having branched pectoral fin rays; from Brachypterois in having D spines longer than 0.5 times BD; from Parapterois in having A with III spines and 5 soft rays; and from Ebosia in having 3 pre-opercular spines and lacking bony crest above orbit. Further, within the genus Dendrochirus, they differed from Dendrochirus biocellatus (Fowler, 1938) in having 17 P rays and lack of ocelli on D soft portion. Subsequently, it keyed out as D. bellus due to 36 vertical scale rows on body, short snout (SnL < 8% of SL) and body colouration. The other two species in the step, namely, D. brachypterus and D. zebra possess more than 45 vertical scale rows on body, comparatively longer snout (SnL 11%-15% of SL) and darker colouration.

Dendrochirus bellus (Jordan et Hubbs, 1925)
Further comparison of the presently described specimens with remaining two congeners not included in the key, Dendrochirus barberi (Steindachner, 1900) and Dendrochirus tuamotuensis Motsunuma et Motomura, 2013 (see Matsunuma and Motomura 2013) revealed marked differences in the number of D rays (10 vs. 9 each in the latter two species) and P rays (17 vs. 18 and 19, respectively in the latter two species). In addition, these two species possess comparatively narrow head (HW 13.8%-17.2% of SL and 12.9% of SL, respectively), longer snout (SnL 9.9%-13.3% of SL and 11.1% of SL, respectively), and longer C fin (32.3%-43.9% of SL and 37.6% of SL, respectively). Remarks. Snyderina is distinguished from closely related genera in having deep body (BD 34% of SL), cycloid body scales, dorsal fin originating anterior to posterior orbital margin, XIII D spines, all spines connected by membrane, V with I spine and 5 soft rays, 13 GR (Poss 1999). This genus comprises two valid species, both of which are distributed in the Northern Indian Ocean (Psomadakis et al. 2015) and western Pacific regions (Kim et al. 2010). Among these, Snyderina guentheri is known from Indian waters (Talwar 1977). Diagnosis. Dorsal fin spines 13, dorsal fin rays 11; anal fin spines 3, anal fin rays 7; pectoral fin rays 13; pelvic fin spine 1, pelvic fin rays 5. Total GR 13. Deep body (BD 34.33% of SL) with long head (HL 48.88% of SL). Light brown coloured with densely arranged bright red spots, four irregular light brown blotches on sides. D light brown with two broad black blotches, remaining fins black. Description. Dorsal fin spines 13, dorsal fin rays 11; anal fin spines 3, anal fin rays 7; pectoral fin rays 13; pelvic fin spine 1, pelvic fin rays 5. Total GR 13. Body deep (BD 34.33% of SL), slender (BW 22.22% of SL), light brown coloured with densely arranged bright red spots and four irregular light brown blotches on sides. Head long (HL 48.88% of SL) with short snout (SnL 8.67% of SL). Mouth moderately large (UJL 15.37% of SL), gape oblique, lower jaw projecting. Jaw teeth villiform, in bands. Eyes small (ED 6.22% of SL), IOW 6.88% of SL. Chin with three pairs of sensory pores, lower lip with one pair of pores. Lacrimal bone with short downward pointing spine and long posterior spine reaching behind middle of eye. Sub-orbital ridge strong. Pre-opercle with one backwardly directed spine. Scales minute, granular. Lateral line complete. D origin above middle of eye (PDL 9.47% of SL). D low (longest D spine 26.79% of SL; longest D ray 25.86% of SL), D base very long (89.63% of SL), membranes between spines incised up to mid height; colouration light brown with bright red spots and two broad black blotches, first between bases of 6-9 spines, second on soft rayed portion. P origin under fifth D spine (PPL 33.23% of SL). P long (longest P ray 35.66% of SL), reaches beyond A origin, middle rays longest, P base short (10.70% of SL). V origin slightly posterior to pectoral insertion. V short (V spine 18.76% of SL; longest V ray 23.54% of SL), not reaching A origin. A origin under last D spine (PAL 64.40% of SL). A short (longest A spine 22.71% of SL; longest A ray 23.18% of SL), A base long (29.87% of SL). Caudal peduncle long (CPL 10.43% of SL), slender (CPW 1.91% of SL), moderately deep (CPD 7.74% of SL). C long (33.88% of SL). P, V, A, C black. Distribution. Previously known from Gulf of Aden, Gulf of Oman, Pakistan (Psomadakis et al. 2015) and southwest coast of India (Talwar 1977). This specimen represents the first record off the East coast of India, and the first outside the known geographical range. Remarks. The presently described specimen was compared with recent descriptions of Snyderina guentheri (see Talwar 1977) and S. yamanokami (see Kim et al. 2010). This specimen closely resembles S. guentheri in morphometric attributes, fin counts and body colouration. On the other hand, S. yamanokami has a deeper body (BD 44.9 % of SL) with longer head (HL 37.6 % of SL- Kim et al. 2010). Moreover, in S. yamanokami, pectoral, pelvic, anal and caudal fins are light pink coloured with large red spots and small black spots; distinct black blotch present in the anterior part of lateral line above pectoral fin (Kim et al. 2010 Remarks. Acropoma is distinguished from closely related genera in the position of anus closer to V origin than A origin, and the presence of luminescent organ between the pelvic fins (Okamoto 2014). This genus comprises six valid species, all of which are distributed in the Indo-West Pacific regions (Okamoto 2014). Among these, two species namely Acropoma japonicum and Acropoma argentistigma Okamoto et Ida, 2002 are known from the Indian waters (Okamoto 2014 Diagnosis. First dorsal fin spines 7; second dorsal fin spine 1, second dorsal fin rays 9; anal fin spines 3, anal fin rays 7; pectoral fin rays 16; pelvic fin spine 1, pelvic fin rays 5. Luminous gland U-shaped, extends between the pelvic fins, anterior end commences before V origin.

Snyderina guentheri (Boulenger, 1889)
Description. First dorsal fin spines 7; second dorsal fin spine 1, second dorsal fin rays 9; anal fin spines 3, anal fin rays 7; pectoral fin rays 16; pelvic fin spine 1, pelvic fin rays 5. Total GR 15. Body slender (BD 34.18% of SL, BW 14.82% of SL), head, dorsal and caudal fins pinkish, lateral sides and lower fins silvery, covered with deciduous scales. Head large (HL 45.09% of SL, HW 15.05% of SL, HH 27.41% of SL). Mouth large (UJL 17.01% of SL; LJL 16.01% of SL), gape strongly oblique. Jaw teeth caniniform, upper jaw with pair of enlarged canines. Eye (ED 10.83% of SL) larger than snout (SnL 9.14% of SL), IOW 7.71% of SL, post-orbital length 24.33% of SL. D 1 origin posterior to pectoral fin insertion (PD 1 L 40.41% of SL). D 1 low, spinous (longest D 1 spine 19.18% of SL), D 1 base short (16.32% of SL). D 2 origin far posterior to level of anus (PD 2 L 64.47% of SL). D 2 low (D 2 spine 4.74% of SL; longest D 2 ray 14.29% of SL), D 2 base short (16.10% of SL). P long (longest P ray 30.47% of SL), transparent. V origin at level of pectoral insertion (PVL 36.12 % of SL). V short (V spine 11.89% of SL; longest V ray 17.91% of SL). Anus blackish, immediately behind V origin (pre-anus length 42.65% of SL). Luminous gland short (14.97% of SL), U-shaped, located between pelvic fins, anterior end commences shortly before V origin. A origin well behind anus (PAL 69.85% of SL). A low (longest A spine 8.95% of SL; longest A ray 13.66% of SL), A base short (11.22% of SL). Lower flanks extending from isthmus to A black; breast and lower flanks dotted with several rows of chromatophores. Caudal peduncle elongate (CPL 16.47% of SL), deep (CPD 18.18% of SL). C forked, short (21.03% of SL). Distribution. Previously known from east coast of Africa to Japan and Australia (Fischer and Bianchi 1984). In the Indian region, Acropoma japonicum was previously reported off the west coast of India (Fischer and Bianchi 1984). This specimen represents the first record off the east coast of India. Remarks. The identification of the presently described specimen following the dichotomous key to species of the genus Acropoma (see Okamoto 2014) revealed that in the first step, the specimen differed from Acropoma lecorneti Fourmanoir, 1988 in having an elongated luminous gland (O-shaped in the latter species). In the second step, the specimen differs from two species, Acropoma boholensis Yamanoue et Matsuura, 2002 and Acropoma hanedai Matsubara, 1953 in having U-shaped luminous gland (in the latter two species, the anterior ends of the gland extend to isthmus). In the third step, it differs from Acropoma profundum Okamoto, 2014 in having the posterior ends of the luminous gland extending slightly beyond anus, but distant from A origin (in the latter species, posterior end extend close to A origin). In the fourth step, the specimen keys out as A. japonicum owing to anterior end of luminous gland placed slightly in advance of V origin; in A. argentistigma the front edge of luminous gland commences at V origin. Remarks. Gymnocranius is distinguished from closely related genera in having scaly cheek, smooth maxilla, D and A fins with 10 soft rays and pointed C lobes (Carpenter and Allen 1989). This genus comprises ten valid species, all of which are distributed in the Indo-Pacific regions (Carpenter and Allen 1989, Borsa et al. 2010, 2013. Among these, three species namely Gymnocranius elongatus; Gymnocranius grandoculis (Valenciennes, 1830); and Gymnocranius griseus (Temminck et Schlegel, 1843) are known from the Indian waters (Rao et al. 2000).

Gymnocranius elongatus Senta, 1973
Fig. 2F Gymnocranius elongatus Senta, 1973: 135, 4  Diagnosis. Dorsal fin spines 10, dorsal fin rays 10; anal fin spines 3, anal fin rays 10; pectoral fin rays 13; pelvic fin spine 1, pelvic fin rays 5. LS 47. Total gill rakers 18. Lower edge of eye crossing line joining snout tip and C fork. C strongly forked, median rays shorter than ED. Description. Dorsal fin spines 10, dorsal fin rays 10; anal fin spines 3, anal fin rays 10; pectoral fin rays 13; pelvic fin spine 1, pelvic fin rays 5. LS 47. Total GR 18. Body deep (BD at D origin 43.07% of SL, BD at A origin 39.48% of SL), silver coloured along flanks and belly, back brownish. Head large (HL 35.26% of SL) with moderately large snout (SnL 10.30% of SL). Mouth moderately large, gape slightly oblique. Upper jaw with band of villiform teeth, lower jaw with slender canines in outer row, inner rows villiform. Eye large (ED 11.93% of SL), its lower edge crossing line joining snout tip and C fork, IOW 9.70% of SL. Single brown band crossing eye, two oblique bands on nape. Scales ctenoid, seven scale rows between D origin and lateral line. D origin far posterior to head (PDL 40.42% of SL). D short (longest D spine 15.28% of SL; longest D ray 14.07% of SL), brown coloured with two prominent and one faint band across it. P transparent, long (longest P ray 26.51% of SL), not reaching A origin. V origin posterior to P origin (PVL 36.23% of SL), V long (V spine 18.96% of SL; longest V ray 28.70% of SL). A origin at level of last D spine (PAL 64.48% of SL), A short (longest A spine 9.73% of SL; longest A ray 12.10% of SL), brown coloured. Caudal peduncle with one oblique band. C strongly forked, moderately long (32.64% of SL) with alternating light and dark brown bands on both lobes, C tips reddish; median rays shorter than ED. Distribution. Previously known from Japan, South China Sea, Sarawak, Andaman Sea (Senta 1973), Australia, and south-western Pacific regions (Carpenter and Allen 1989). In India, Rao et al. (2000) reported Gymnocranius elongatus from Rutland Island (South Andaman). This specimen represents the first record off the Indian mainland. Remarks. The identification of the presently described specimen following the dichotomous key to species of the genus Gymnocranius (see Carpenter and Allen 1989) revealed that in the first step, the specimen keyed out as G. elongatus owing to lower edge of eye crossing line joining snout tip and C fork, and strongly forked C with median rays shorter than ED. On the other hand, in the seven other congeners represented in this key (Gymnocranius euanus (Günther, 1879); Gymnocranius audleyi Ogilby, 1916; Gymnocranius frenatus Bleeker, 1873; "Gymnocranius sp."; G. griseus; Gymnocranius microdon (Bleeker, 1851); and G. grandoculis), the lower edge of eye is distinctly above line joining snout tip and C fork. Additionally, these species possess moderately forked C with median rays longer than ED. A recent taxonomic paper (Borsa et al. 2013) re-described "Gymnocranius sp." of Carpenter and Allen (1989) as Gymnocranius satoi Borsa, Béarez, Paijo et Chen, 2013. The comparison of the presently described specimen with two more recently described species, Gymnocranius oblongus Borsa, Béarez et Chen, 2010 (see Borsa et al. 2010) and Gymnocranius superciliosus Borsa, Béarez, Paijo et Chen, 2013 (see Borsa et al. 2013) revealed that it differed from the latter two species in lower edge of eye crossing line joining snout tip and C fork. Moreover, it differed from Gymnocranius superciliosus Borsa, Béarez, Paijo et Chen, 2013 in having pointed C lobes. It is noteworthy that the C lobes of G. oblongus juveniles are similar to those of G. elongatus, whereas adults have rounded C lobes.

Pristotis cyanostigma Rüppell, 1838
Cheek below eye scaleless. Two pairs of anterior jaw teeth enlarged and caniniform, canines present at corner of mouth. Complete lateral line with less than 28 scales, 4 scale rows between lateral line and D origin. D with IX spines and 11-12 soft rays, A with III spines (Westneat 2001). This genus comprises five valid species, all of which are distributed in the Indo-West Pacific regions (Randall 1996). Among these, two species namely Leptojulis chrysotaenia Randall et Ferraris, 1981 and L. cyanopleura are known from Indian waters (Randall 1996). Diagnosis. Dorsal fin spines 9, dorsal fin rays 11; anal fin spines 3, anal fin rays 11; pectoral fin rays 13; pelvic fin spine 1, pelvic fin rays 5. LS 27. Total GR 27. Body elongate (BD 2.66 times in SL), yellow coloured with two longitudinal brown stripe on sides, upper stripe just below D fin and one mid-lateral stripe extending from snout to caudal peduncle. Head small (HL 4.21 times in SL). Pectoral fin short (16.04% of HL). Description. Dorsal fin spines 9, dorsal fin rays 11; anal fin spines 3, anal fin rays 11; pectoral fin rays 13; pelvic fin spine 1, pelvic fin rays 5. Total GR 27. Body elongate (BD 37.63% of SL), slender (BW 9.87% of SL), yellow coloured with two longitudinal brown stripes on sides, upper stripe just below dorsal fin and one mid-lateral stripe extending from snout to caudal peduncle. Head small (HL 23.75% of SL), with small eye (ED 7.75% of SL), IOW 8.50% of SL. Mouth small (UJL 6.33% of SL), terminal. Jaws with short caniniform teeth, anterior-most four teeth large canines. Snout short (SnL 6.38% of SL). Lateral line close to dorsal fin base in its anterior twothirds, descending abruptly and continuing along midlateral stripe in its posterior one-third, scales in lateral line 27. Scales large, cycloid, two scale rows between D origin and lateral line; scale rows between stripes brownish. D origin behind head (PDL 26.37% of SL). D short (longest D spine 11.10% of SL; longest D ray 11.67% of SL), D base long (63.94% of SL). A origin at level of first D ray (PAL 54.37% of SL), A short (longest A spine 11.66% of SL; longest A ray 10.58% of SL), A base long (34.38% of SL). P short (longest P ray 16.04% of SL). V origin slightly behind pectoral insertion (PVL 37.63% of SL). V short (V spine 5.77% of SL, longest V ray14.22% of SL). Caudal peduncle short (CPL 9.59% of SL) and deep (CPD 15.51% of SL). C short (14.15% of SL), rounded. D, A, V, and C light orange coloured, P transparent. Distribution. Previously known from the Persian Gulf to Malaysia, Indonesia, New Guinea, and Australia (Randall 1996). In India, Randall (1996) reported Leptojulis cyanopleura from Vizhinjam (Kerala). This specimen represents the first record along the East coast of India. Remarks. The identification of the presently described specimen following the dichotomous key to species of the genus Leptojulis (see Randall 1996) revealed that in the first step, the specimen differed from Leptojulis polylepis Randall, 1996 in having 27 lateral line scales (46 in the latter species). In the second step, this specimen differed from Leptojulis lambdastigma Randall et Ferraris, 1981 in having short P fin, D and A with 11 soft rays, and absence of V-shape mark on nape. On the other hand, L. lambdastigma possesses longer P fin, D and A with 12 soft rays, and V-shaped mark on nape. In the third step, it differed from L. chrysotaenia in having an elongate body (BD 2.66 times in SL and smaller head (HL 4.21 times in SL). In the fourth step, the specimen keyed out as L. cyanopleura owing to 27 gill rakers and absence of dark spot on C base. The other species in the fourth step, Leptojulis urostigma Randall, 1996 possesses 16-18 gill rakers and dark brown spot on C base.

Family Acanthuridae Bonaparte, 1835
Genus Naso Lacépède, 1801 Naso Lacépède, 1801: 105 (type species: Naso fronticornis Lacépède, 1801, by subsequent designation). Remarks. Naso is distinguished from closely related genera in having shallow caudal peduncle (depth 4.0-6.0 times in head length), 1-2 bony plates on either sides on caudal peduncle, D with IV-V spines, V with I spine and 3 soft rays (Randall 2001a). This genus comprises twenty species distributed in the Indo-Pacific regions (Randall 2001b, Johnson 2002, Ho et al. 2011. Among these, seven species namely Naso brachycentron (Valenciennes, 1835); Naso brevirostris (Cuvier, 1829); Naso hexacanthus (Bleeker, 1855); Naso lituratus (Forster, 1801); Naso tuberosus Lacepède, 1801; Naso unicornis (Forsskål, 1775); and Naso vlamingii (Valenciennes, 1835) are known from the Indian waters (Sluka 2013, Froese andPauly 2016). Diagnosis. Dorsal fin spines 5, dorsal fin rays 29; anal fin spines 2, anal fin rays 27; pectoral fin rays 15; pelvic fin spine 1, pelvic fin rays 3. Body deep (BD 2.11 times in SL). Teeth incisiform with finely serrate edges. Dorsal surface of snout angled at 54° with base of snout, lacking protuberance. Dorsal surface without hump, profile beneath spinous portion of dorsal fin slightly convex. Caudal peduncle with two bony plates on either side. C with white posterior margin. Description. Dorsal fin spines 5, dorsal fin rays 29; anal fin spines 2, anal fin rays 27; pectoral fin rays 15; pelvic fin spine 1, pelvic fin rays 3. Body deep (BD 42.21%-47.40% of SL), compressed (BW 14.23%-14.52% of SL), drab grey coloured. Head small (HL 26.44%-29.29% of SL) with large eye (ED 8.88%-11.30% of SL), IOW 8.47%-9.56% of SL, sub-orbital width 11.34%-11.69% of SL. Mouth small (UJL 5.77%-5.85% of SL), terminal. Jaw teeth pointed incisors, with serrate edges. Snout moderately long (SnL 12.00%-12.46% of SL). Dorsal surface of snout angled at 54° with base of snout, lacking protuberance. Oblique groove on side of snout extends from anterior edge of orbit half-way to mouth. Scales minute, ctenoid. Dorsal profile of back below spinous dorsal fin slightly arched. Lateral line parallel to dorsal profile of body. D origin slightly anterior to opercular margin (PDL 23.76%-28.67% of SL). D short (first D spine 13.20%-16.32% of SL; second D spine 11.68%-16.14% of SL; fifth D spine 10.31%-12.48% of SL; longest D ray 12.05%-12.40% of SL), black coloured, D base long (66.80%-66.81% of SL). A origin under fifth D spine (PAL 37.16%-37.28% of SL). A short (first A spine 7.17%-11.60% of SL; second A spine 7.38%-9.53% of SL; longest A ray 9.34%-9.53% of SL), black coloured, A base long (53.50%-54.20% of SL). P short (longest P ray 17.30%-19.61% of SL), transparent, its origin under operculum. V origin under pectoral insertion (PVL 21.85%-24.41% of SL). V short (V spine 10.74%-11.47% of SL; longest V ray 12.14%-14.06% of SL), grey coloured, reaching beyond A origin. Caudal peduncle short (CPL 6.76%-9.49% of SL), slender (CPW 4.15%-4.65% of SL; CPD 8.74%-9.59% of SL), with two keeled plates on either side. C moderately long (20.99%-23.63% of SL), emarginated, grey coloured, with white posterior margin; C fork short (9.86%-12.57% of SL). Distribution. Previously known from East coast of Africa (Smith and Heemstra 1986) to Hawaii (Robertson et al. 2004). This specimen represents the first record off the Indian mainland. Remarks. The identification of the presently described specimen following the dichotomous key to species of the genus Naso (see Randall 2001b) revealed that in the first step, the specimen shared the character "two keeled plates on each side of caudal peduncle" with 14 species in the key. In the second step, this specimen differed from Naso lituratus and Naso elegans (Rüppell, 1829) in having incisiform teeth with serrated edges, grey coloured peduncular plates and absence of yellow line on head. The specimen being a juvenile could not be compared in respect of protuberance or horn on snout. Further, it differed from N. brachycentron in lacking dorsal hump and having slightly convex profile beneath spinous portion of dorsal fin; it differed from N. unicornis in having dorsal profile of snout at an angle of 54° and grey peduncular plates. Subsequently, it keyed out as N. annulatus owing to V dorsal spines, plain grey coloured body and C with white posterior margin. The comparison of the presently described specimen with three species not included in Randall's key namely Naso mcdadei Johnson, 2002; Naso tonganus (Valenciennes, 1835) (see Johnson 2002); and Naso tergus Ho, Shen et Chang, 2011(see Ho et al. 2011) revealed that it differed from N. tergus in having five D spines (six in the latter species). Further, it differed from the latter three species in having a deeper body, longer head, larger eye and longer P fin. The morphometric proportions of BD, HL, ED, and P lengths for N. mcdadei are 33.6%-38.4%, 20.8%-24.4%, 4.2%-7.0%, and 13.1%-16.5%, respectively; for N. tonganus, 34.4%-41.1%, 20.8%-26.4%, 4.4%-6.0%, and 13.7%-17.2%, respectively; for N. tergus, 34.4%-36.8%, 24.6%-26.6%, 6.3%-7.2%, and 14.0%-15.7%, respectively. Diagnosis. Dorsal fin spines 4, dorsal fin rays 29; anal fin spines 2, anal fin rays 27; pectoral fin rays 16; pelvic fin spine 1, pelvic fin rays 3, total GR 25. Body slender (BD 3.25 times in SL). Snout profile convex; oblique groove on side of snout extends from anterior edge of orbit half-way to mouth. Inter-orbital region and internarial space flat. Caudal peduncle with one bony plate on either side. Description. Dorsal fin spines 4, dorsal fin rays 29; anal fin spines 2, anal fin rays 27; pectoral fin rays 16; pelvic fin spine 1, pelvic fin rays 3, total GR 25. Body less deep (BD 30.80% of SL), compressed (BW 11.46% of SL), drab grey coloured, with lighter patches on upper half of body. Head small (HL 25.36% of SL), anterior profile convex, lacking protuberance. Eye moderately large (ED 8.21% of SL), IOW 7.90% of SL, sub-orbital width 9.46% of SL. Mouth small (UJL 2.98% of SL), terminal. Jaw teeth pointed incisors, with serrate edges. Snout moderately long (SnL 11.56% of SL). Oblique groove on side of snout extending from anterior edge of orbit half-way to mouth. Inter-orbital region and inter-narial space flat. Scales minute, ctenoid. Dorsal profile of back below spinous dorsal fin slightly flat. Lateral line parallel to dorsal profile of body. D origin slightly anterior to opercular margin (PDL 26.08% of SL). D short (first D spine 6.95% of SL; second D spine 10.20% of SL, longest D ray 9.39% of SL), black coloured, D base long (63.10% of SL). A origin under fourth D spine (PAL 34.88% of SL). A short (first A spine broken; second A spine 5.95% of SL; longest A ray 9.12% of SL), black coloured, A base long (54.26% of SL). P short (longest P ray 15.75% of SL), transparent, P origin under operculum. V origin under pectoral insertion (PVL 24.08% of SL). V short (V spine 9.25% of SL; V longest ray 9.81% of SL), grey coloured, reaching beyond A origin. Caudal peduncle short (CPL 8.86% of SL), slender (CPW 3.48% of SL; CPD 5.18% of SL), with one keeled plate on either side. C moderately long (19.65% of SL), emarginated, grey coloured, with white posterior margin; C fork short (6.32% of SL). Distribution. East coast of Africa to Japan, Solomon Islands, and Caroline Islands (Randall 1994). This specimen represents the first record in the Indian waters. Remarks. The identification of the presently described specimen following the dichotomous key to species of the genus Naso (see Randall 2001b) revealed that in the first step, the specimen shared the character "one keeled plate on each side of caudal peduncle" with three species in the key. In the second step, this specimen differed from Naso minor (Smith, 1966) in having four dorsal spines (five in the latter species) and long groove on side of snout extending from near edge of orbit halfway to mouth (in N. minor, the groove is shorter). In the third step, it keys out as N. thynnoides owing to slender body (BD 3.25 times in SL), convex snout, and flat median zone on anterior inter-orbital and inter-narial spaces. It differs from Naso caeruleacauda Randall, 1994 with deeper body (BD 2.75-2.80 times in SL), straight snout, and strongly convex inter-orbital and inter-narial spaces. The presently described specimen differed slightly from Randall's description of N. thynnoides (see Randall 1994) in respect of three morphometric ratios (SL/BD, SL/HL, and HL/SnL). The observed ratios were 3.25, 3.94, and 2.19, respectively as compared to 2. 80-3.20, 4.05-4.20, and 1.95-2.10, respectively reported by Randall (1994 Remarks. Pseudalutarius is a monotypic genus distinguished from closely related genera in the forward position of D 1 . It is distributed from the eastern coasts of Africa to southern Japan, northern Australia and New Caledonia (Matsuura 2015). The presently reported observation constitutes the first record from Indian waters. Description. Dorsal fin spines 2, dorsal fin rays 43; anal fin rays 41; pectoral fin rays 12. Body less deep (BD 28.28% of SL), compressed (BW 10.03% of SL), off white coloured with two longitudinal brown bands along sides. Head moderately large (HL 28.41% of SL), gently sloping forward. Mouth small, terminal. Jaw teeth long, incisiform. Eye moderately large (ED 6.97% of SL), IOW 7.62% of SL. Gill slits long (4.83% of SL). Snout long (SnL 18.74% of SL). Scales minute, prickly, embedded in skin. Two dorsal fins, D 1 origin anterior to eye (snout to dorsal spine distance 11.55% of SL). Lower jaw to V rudiment distance 44.58% of SL. V rudiment concealed under skin. D 1 spine extremely long (29.17% of SL); inter-dorsal space 35.58% of SL. D 2 base moderately long (39.72% of SL); longest D ray 5.18% of SL. A origin posterior to D 2 origin (PAL 53.78% of SL). A base moderately long (38.46% of SL), longest A ray 7.13% of SL. P transparent, short (longest P ray 7.10% of SL). Caudal peduncle short (CPL 5.18% of SL), slender (CPD 6.84% of SL). C moderately long (14.54% of SL), prominently dark brown. Distribution. East Africa to southern Japan, northern Australia and New Caledonia (Matsuura 2015). This specimen represents the first record in the Indian waters.

Pseudalutarius nasicornis
Remarks. Pseudalutarius nasicornis is the only known representative of the genus Pseudalutarius. It differs from other monacanthids in having a long, slender body and D 1 placed well in advance of the eye (Hutchins 2001 Remarks. Lagocephalus is distinguished from closely related genera in having lower half of body silver white, contrasted to dark dorsal half, terminal mouth, indistinct chin, nasal organ covered by small sac with two nostrils, top of P base below lower margin of eye, D and A with 9-10 soft rays, raised skin fold along lower side of caudal peduncle (Matsuura 2001 GB.43.6.15.10,(1,124.42 mm SL), by-catch landed at Tuticorin fisheries jetty, 15 March 2013. Diagnosis. Body sub-cylindrical, dorsal and upper half of lateral surfaces greenish yellow covered with unequal sized dark spots, lateral silver band extending from mouth to C fin. Prickly area on dorsal surface commencing posterior to eye, extending up to D origin. Raised skin fold extending from chin to caudal fin base. Description. Dorsal fin rays 10; anal fin rays 9; pectoral fin rays 15. Body sub-cylindrical (BW at P base 16.20% of SL), shallow (maximum BD 17.77% of SL; BD at end of D base 9.93% of SL), dorsal and upper half of lateral surfaces greenish yellow covered with unequal sized dark spots, silver band on lower flanks extending from mouth to caudal fin, ventral surface whitish. Head moderately large (HL 29.98% of SL). Mouth small, terminal (width 6.22% of SL; upper lip depth 2.44% of SL). Teeth fused to form two plates in each jaw, with anterior beak-like projection. Snout long (SnL 12.72% of SL), snout to anterior edge of nasal organ distance 6.94% of SL. Nasal organ extremely small (length 0.94% of SL), located in depression, covered by small sac with two nostrils; posterior edge of nasal organ to anterior edge of eye distance 4.30% of SL. Eye moderately large (ED 10.42% of SL), IOW 4.73% of SL, preceded by silvery patch. Gill slit long (8.33% of SL). Patch of spinules on dorsal surface commencing posterior to eye, extending up to D origin. Two lateral lines. D origin at level of anus (snout to D origin distance 66.87% of SL). D base short (6.33% of SL); longest D ray 11.84% of SL. Raised skin on lateral side fold extending from chin to C base. Patch of spinules on belly extending posteriorly up to cloaca. A origin posterior to D origin (snout to A origin distance 68.16% of SL). A base short (6.27% of SL), longest A ray 11.14% of SL. P transparent, short (longest P ray 16.50% of SL). Caudal peduncle long (CPL 23.02% of SL), tapering (CPD 10.42% of SL). C emarginate, moderately long (17.70% of SL). Distribution. Throughout the Indo-Pacific regions up to Japan (Iwatsubo et al. 2009). This species is a Lessepsian migrant to the Mediterranean with known occurrences off Lebanon, Israel, Turkey, Syria, Greece, Cyprus, Libya, and Egypt (Farrag et al. 2016). This specimen represents the first record in the Indian waters. Remarks. Two out of 11 valid species in the genus Lagocephalus-L. suezensis and Lagocephalus sceleratus (Gmelin, 1789)-are characterized by the presence of two lateral lines and greyish spots on greenish dorsal surface. Among these, L. suezensis attains a smaller size (18.59 cm SL-Iwatsubo et al. 2009) as compared to L. sceleratus (110.00 cm SL-Froese and Pauly 2016). In addition, it has a raised skin fold along lower side of caudal peduncle (absent in L. sceleratus), and unequal-sized grey spots on the dorsal surface (equal-sized spots in L. sceleratus- Farrag et al. 2016   12A. Jaw teeth distinct, pointed. Dorsal fin well in advance of eye, with II spines (first long, second minute), 43 soft rays; anal fin with 41 soft rays…Pseudalutarius nasicornis 12B. Jaw teeth fused to form four dental plates with strong cutting edges. Dorsal fin posterior to mid-point of body, without spines, soft rays 10; anal fin with 9 soft rays. Prickly area on the back extends from behind the eye to dorsal fin origin. Body light greenish dorsally, covered with unequal sized dark spots ......Lagocephalus suezensis

DISCUSSION
The Gulf of Mannar, located off the south-eastern coast of India, is among the biologically richest marine ecosystems in the Indian Ocean region. The presence of myriad numbers of rare reef-associated as well as deep sea fishes suggests that structural complexities among the bottom habitats particularly coral reefs have facilitated the establishment of micro-niches that provide safe haven for diverse assemblages of demersal fishes. Moreover, the development of coastal demersal fisheries and expansion of fishing fleets has recently further enabled the discovery of many rare species (Padate et al. 2014). However, excessive mechanized fishing activity in this fragile biosphere reserve has adversely affected the unique coral reef and sea-grass ecosystems (Diraviya Raj et al. 2017). The presently reported sampling survey corroborated that large mechanized fishing vessels employ bottom trawls to harvest reef fishes and invertebrates in coastal shelf waters, and also use mid-water trawls in deeper offshore waters to harvest tuna and other pelagic fishes. Moreover, several rare reef-associated fishes caught incidentally by shrimp trawlers are regularly dumped at major fishing harbours along the Gulf of Mannar coast as evident from few specimens collected during this study.
In view of this, it was pertinent to document demersal fish fauna affected by mechanized fisheries of the region. This effort comprising only 23 bottom trawl hauls up to 153 m depth revealed seven elasmobranchs and 190 teleostean taxa. These observations confirm the removal of myriad varieties of demersal fishes at an alarming rate. The present observations revealed that among the thirteen new records, the triakid shark genus Hypogaleus and the monacanthid genus Pseudalutarius were recorded for the first time from the Indian region. These observations suggested that unabated alteration of their natural habitats might have reduced the habitat complexity of the fishing grounds thereby rendering these species vulnerable to fishing.
A review of the biogeographical aspects of the newly recorded species revealed that five out of thirteen species had restricted zoogeographical distributions. Dendrochirus bellus was previously known only from the western Pacific regions, Gymnocranius elongatus from the eastern Indian Ocean and western Pacific regions, Pomacentrus similis from the eastern Indian Ocean, and two species (Pristotis cyanostigma and Lagocephalus suezensis) from the Red Sea). The Red Sea region has high endemicity of marine fishes (13.6 %) attributed to its isolation from the Indian Ocean during glacial periods (Eschmeyer et al. 2010). The Indo-Australian archipelago, straddling the eastern Indian Ocean and western Pacific regions, is a complex geographical entity, whose high species diversity and endemicity are attributed to recurring vicariance (geographical separation of a population owing to physical barriers) events during the past 50 million years (Lohman et al. 2011). The present observations make it pertinent to suggest that the Gulf of Mannar region might have experienced vicariance events in the geological past that resulted in the isolation of reef fish populations from similar populations in the Indo-Australian archipelago (Sorenson et al. 2014). Moreover, rapid northward drift of the Indian subcontinent from Africa over the past 200 million years (Yoshida and Hamano 2015), coupled with isolation of the Red Sea during the glacial periods (Eschmeyer et al. 2010) might have contributed to the separation of their respective populations.