Introduction
As a part of various research programmes conducted by the Centre for Marine Living Resources and Ecology (CMLRE), extensive mesopelagic and deep sea demersal trawling operations were carried aboard the Research Vessel (RV) ‘Sagar Sampada’ between the years 2010 and 2017. One of the major objectives of these programmes was to assess the deep sea fishery resources in the Indian EEZ at depths of 200–1000 m. While most of the cruises were confined to the Indian EEZ, cruise 344 of Sagar Sampada sampled a vast area in the western Indian Ocean, between latitudes 12˚54.041′N and 15˚28.009′S. During these cruises, mesopelagic fishes were caught in varying amounts but the vast majority of our mesopelagic fishes were collected during the mesopelagic cruises of 320, 331 and 344, which were aimed at assessing myctophid resources in the western Indian Ocean. In all the mesopelagic cruises, myctophids dominated the collection followed by Stomiiformes and other mesopelagic fishes. A detailed study on myctophids collected during these surveys was carried out by Meera (Reference Meera2018); however, such a study was never been conducted for Stomiiformes until now.
The first breakthrough in the systematic study of Stomiiformes from the Indian Ocean was from deep sea ichthyological expeditions led by Alcock (Reference Alcock1899) and Brauer (Reference Brauer1906). Later many significant contributions have come out as a part of International Indian Ocean Expedition (e.g. Gibbs and Hurwitz, Reference Gibbs and Hurwitz1967; Goodyear and Gibbs, Reference Goodyear and Gibbs1970). Smith and Heemstra (Reference Smith and Heemstra1986) gave a detailed report on Stomiiformes collected from South Africa. Several revisionary studies as well as new descriptions had come from the Indian Ocean with efforts of Russian Ichthyologists like Parin, Mukhacheva and Borodulina (e.g. Parin and Pokhilskaya, Reference Parin and Pokhilskaya1978; Mukhacheva, Reference Mukhacheva1981; Parin and Borodulina, Reference Parin and Borodulina2003). Nevertheless, Stomiiformes is among the least studied fishes from the Indian EEZ with 29 species (Table 1) reported so far.
Table 1. List of stomiiform fishes reported from India
Nine of the collected stomiiform fishes were new to Indian EEZ whose descriptions are provided below. The rest of the species, including ones taken from the western Indian Ocean, were already reported from respective areas and so detailed description has been omitted. However, a list of all the stomiiform species collected during these cruises is provided in the discussion.
Materials and methods
Fishes were collected on board the fisheries and oceanographic RV ‘Sagar Sampada’ during the cruises 280, 281, 292, 320, 321, 331, 344 and 367 from 2012 to 2017. Most of the collection was made using 49.5 m cosmos trawl and remaining with 28 and 45 m midwater trawls with cod end mesh sizes of 10 and 25 mm, respectively. Sampling was carried out as horizontal tows along the deep scattering layer, delineated through acoustics using SIMRAD EK 60. Trawling operations continued for 30–120 min at a speed of 0.5–3 knots. The entire catch was carefully sorted and relevant specimens preserved in formalin for further studies. If necessary, subsampling was performed in proportional to number of individuals of each species. In addition to the aforementioned gears, a few stomiiform fishes also came up in demersal catches using high speed demersal trawl. Station information is given in Table 2.
Table 2. List of stations sampled by R/V Sagar Sampada along India and western Indian Ocean
Morphometric measurements and meristic counts followed Smith and Heemstra (Reference Smith and Heemstra1986), except for Sternoptychidae, which followed Baird (Reference Baird1971), Badcock and Baird (Reference Badcock and Baird1980) and Harold (Reference Harold1994). Values are given in ranges whenever the specimen count was more than two, whenever there were only 1–2 specimens, the counts of single or both the specimens were given in the order as that of material examined. Photophore terminology follows Morrow (Reference Morrow, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964a, Reference Morrow, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964b) and Smith and Heemstra (Reference Smith and Heemstra1986) except for Sternoptychidae, which follow Baird (Reference Baird1971), Badcock and Baird (Reference Badcock and Baird1980) and Harold (Reference Harold1994). All the specimens were stored in 7–8% formalin and deposited in CMLRE reference centre under the voucher ID series ‘IO/SS/FIS/00xxx’. Standard length and station ID follows the voucher number, including the ones in Table 5. Number of specimens under a single accession number is given in parenthesis when more than one specimen was stored under a same number.
Abbreviations: HL, head length; ED, eye diameter; SL, standard length; HSDT, high speed demersal trawl; MWT, mid water trawl. Voucher ID abbreviations: IO, Indian Ocean; SS, Sagar Sampada; FIS, fish.
Results
Systematics
Order Stomiiformes Tables 3, 4; Figures 1–4
Family Stomiidae Bleeker, 1859
Genus Photonectes Günther, 1887
Photonectes paxtoni Flynn and Klepadlo, Reference Flynn and Klepadlo2012
Total two specimens. IO/SS/FIS/00570, 80 mm, 32009, Figure 1a; IO/SS/FIS/00571, 70 mm, 32004. This is the first finding of P. paxtoni in the Indian Ocean.
Figure 1. (a) Photonectes paxtoni, IO/SS/FIS/00570; (b) Photonectes barnetti, IO/SS/FIS/00524; (c) Melanostomias valdiviae, IO/SS/FIS/00535; (d) Borostomias elucens, IO/SS/FIS/00531; (e) Grammatostomias dentatus, IO/SS/FIS/00732; (f) Ichthyococcus parini, IO/SS/FIS/00574; (g) Polyipnus limatulus, IO/SS/FIS/00601; (h) Argyropelecus sladeni, IO/SS/FIS/00588; (i) Sternoptyx obscura, IO/SS/FIS/00595. Scale bar 3 cm. All photos of specimens preserved in formalin.
Figure 2. An illustration of the roof of mouth of gonostomatid Sigmops elongatus showing various groups of teeth, the two grey ovals depict the orbital region. The superficial teeth found in many Stomiiformes commonly called pterygoid teeth are also marked.
Figure 3. Catch localities of new records of Stomiiformes from India.
Figure 4. Barbels of (a) Melanostomias valdiviae; (b) Borostomias elucens; (c) Photonectes barnetti, IO/SS/FIS/00710; (d–f) Photonectes paxtoni: (d) IO/SS/FIS/00570, (e) IO/SS/FIS/00571, (f) figure representing barbel regeneration, here barbels of IO/SS/FIS/00570 and IO/SS/FIS/00571 are super imposed and compared, dotted lines indicate the expected growth pattern from regenerating barbel, arrows indicate direction of growth; (g–i) Melanostomias melanops: (g) entire M. melanops barbel, (h) terminal tip of IO/SS/FIS/00539 231 mm SL, (i) terminal tip of IO/SS/FIS/00539 198 mm SL, (j) Aristostomias xenostoma.
Table 3. Meristic and morphometric counts of newly recorded stomiids from India
Empty cells indicate that the respective feature is not taxonomically relevant for this species.
Table 4. Meristic and inter orbital counts of newly recorded sternoptychids and phosichthyids
Empty cells indicate that the respective feature is not taxonomically relevant for this species.
Specimen diagnosis
The specimens belonged to braueri–caerulescens complex within the subgenus Photonectes (Prokofiev, Reference Prokofiev2019) as they had biserial heterogeneous dentition along premaxilla, heterogeneous dentition in lower jaw and development of skin over the rays of vertical fins. The specimens were confirmed as Photonectes paxtoni since it is the only species in the braueri–caerulescens complex characterized by a short barbel (50% of head length) terminating in a large ovoid bulb (Flynn and Klepadlo, Reference Flynn and Klepadlo2012; Prokofiev, Reference Prokofiev2019). Furthermore, the specimens lacked pectoral fins and any blue luminous tissues on body, yet another two characters of P. paxtoni (Flynn and Klepadlo, Reference Flynn and Klepadlo2012; Prokofiev, Reference Prokofiev2019). Counts and measurements of our specimens are summarized in Table 3.
Description
PO triangular; gill filaments long, three times the gill arch depth; dorsal and anal fin rays covered by skin at least half the length of the ray, anterior fin rays are more densely covered than the posterior rays. Barbel short, 50% HL. In IO/SS/FIS/00570, the barbel terminates in a large, white bulb with slightly sharper edges on the ventral side (Figure 4d). In specimen IO/SS/FIS/00571, the bulb seems to be underdeveloped, the barbel expands and abruptly tapers, giving rise to a luminescent area resembling a broad ‘V’ shape (Figure 4e).
Remarks
Photonectes paxtoni is a rare stomiid known only from three juvenile specimens taken from Pacific Ocean near New Guinea (Flynn and Klepadlo, Reference Flynn and Klepadlo2012; Prokofiev, Reference Prokofiev2014, Reference Prokofiev2019). There were few differences in photophore counts and vertical fin ray counts in present specimens with original description (Flynn and Klepadlo, Reference Flynn and Klepadlo2012). This, along with longer gill filaments, can be attributed to intra-specific variability of the populations living in two different oceans. Prokofiev (Reference Prokofiev2019) reported such variations in length of gill filaments. The barbel lengths of both the specimens were 50% HL, which corresponds to that of holotype and paratype, indicating that the barbel length is a stable character throughout the ontogeny of the animal. The bulbs of the present specimens were not identical to each other. The aberrant bulb of IO/SS/FIS/00571 is small compared to IO/SS/FIS/00570 which is probably due to regeneration or a variation. Whatever be the reason, in close comparison it was noted that there is amazing similarity between the two bulbs, shown in the drawing of Figure 4f. Prokofiev (Reference Prokofiev2015, Reference Prokofiev2019) has reported cases of barbel regeneration in P. margarita (Goode and Bean, 1896) and P. filipendulus Prokofiev, Reference Prokofiev2019.
Photonectes barnetti Klepadlo, Reference Klepadlo2011
Total of four specimens. IO/SS/FIS/00524, 213 mm, 36708, Figure 1b; IO/SS/FIS/00525, 159 mm, 29205; IO/SS/FIS/00526, 126 mm, 28016; IO/SS/FIS/00710, 200 mm, 31601. This is the first record of P. barnetti from the Indian Ocean.
Specimen diagnosis
The specimens showed characteristic features of species belonging to albipennis-group within the subgenus Photonectes (Prokofiev, Reference Prokofiev2019); these are biserial heterogeneous dentition along the premaxilla, IP photophores placed away from tip of isthmus and absence of skin along the vertical fins. The specimens were confirmed as P. barnetti mainly by their barbel morphology (Figure 4c). The barbel of our fishes were longer than head and consisted of two luminous areas, a distal bulb and a proximal bulb like swollen area at about mid length of barbel. The latter mentioned luminous area is only as thick as the stem above and had a longitudinal line of black pigment running through one side of this area. This type of barbel is typical of P. barnetti, additionally the specimens lacked any blue luminous tissues in body and had two small luminous spots at the upper operculum, all indicative of P. barnetti (Klepadlo, Reference Klepadlo2011; Prokofiev, Reference Prokofiev2019). Counts and measurements of our specimens are summarized in Table 3.
Remarks
The relationship between Photonectes barnetti and the highly similar Photonectes coffea Klepadlo, Reference Klepadlo2011 is unclear (Prokofiev, Reference Prokofiev2019). Both the species differ primarily in the pigmented tissue ventrally at the unpigmented area of the barbel (absent in P. coffea) (Prokofiev, Reference Prokofiev2019). The proximal unpigmented area in P. coffea is usually slightly swollen and appears as a bulb; however, the species can also have this bulb as thin as the barbel stem, making that the two species only differ in occurrence of pigmentation in the proximal unpigmented area of the barbel. The barbel of P. barnetti collected from Arabian Sea (IO/SS/FIS/00710) differed as it has an additional smaller unpigmented area between the first unpigmented area and the terminal bulb, also it has the extreme end of barbel unpigmented (Figure 4c). We treat this difference as a variation as uncertainties still exist in relationships between the species in the albipennis-group (Prokofiev, Reference Prokofiev2019) as well as variability in the barbel has been reported in Photonectes albipennis (Döderlein, 1882) (Prokofiev, Reference Prokofiev2019). Previously, P. barnetti was known only from Hawaii and western Pacific Ocean (Klepadlo, Reference Klepadlo2011; Prokofiev, Reference Prokofiev2019).
Genus Melanostomias Brauer, 1902
Melanostomias valdiviae Brauer, 1902
Total seven specimens. IO/SS/FIS/00535, 172 mm, 344Ι08, Figure 1c; IO/SS/FIS/00536 (4), 97–135 mm, 32001; IO/SS/FIS/00537, 75 mm, 32008; IO/SS/FIS/00538, 75 mm, 32004. First record from peninsular India.
Specimen diagnosis
Our specimens are referred to Melanostomias valdiviae based on the small (twice as long as wide) terminal expansion of the barbel bearing three luminous bulbs and the stem of the barbel being pigmented (Figure 4a). The specimens had their main barbel axis transverse through the terminal expansion and lacked any other smaller bulbs along the stem, both of which are important features of M. valdiviae (Parin and Pokhilskaya, Reference Parin and Pokhilskaya1978). Counts and measurements of our specimens are summarized in Table 3.
Remarks
Widely distributed species known from all oceans (Brauer, Reference Brauer1906; Regan, Reference Regan1908; Morrow and Gibbs, Reference Morrow, Gibbs, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964; Parin and Pokhilskaya, Reference Parin and Pokhilskaya1978; Villarins et al., Reference Villarins, Dario, Eduardo, Frédou, Bertrand, Prokofiev and Mincarone2022). The species can be found throughout the Indian Ocean, the holotype was taken from eastern Indian Ocean off Sumatra (Brauer, Reference Brauer1906). Also known from South East Indian Ocean off South Africa (Gibbs, Reference Gibbs, Smith and Heemstra1986), Andaman Sea and southern Arabian Sea (Parin and Pokhilskaya, Reference Parin and Pokhilskaya1978).
Genus Borostomias Regan, Reference Regan1908
Borostomias elucens (Brauer, Reference Brauer1906)
Total five specimens. IO/SS/FIS/00711 (2), 205, 270 mm, 28103; IO/SS/FIS/00531, 276 mm, 344Ι11, Figure 1d; IO/SS/FIS/00532, 200 mm, 344Ι10; IO/SS/FIS/00533, 187 mm, 344ΙΙ04. First record from Indian waters.
Specimen diagnosis
All our specimens are referred to Borostomias elucens based on a highly arched AC row, a simple terminal bulb lacking any photophores in it, which was up to three times long as it is wide (Figure 4b) (Gibbs, Reference Gibbs, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964; Masuda et al., Reference Masuda, Amoaka, Araga, Uyeno and Yoshino1984). Counts and measurements of our specimens are summarized in Table 3.
Remarks
Two of our five specimens had a white coloured barbel instead of black. This is due to damage during collection; Gibbs (Reference Gibbs, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964) has reported such incidents. The species is known from all oceans (Brauer, Reference Brauer1906; Gibbs, Reference Gibbs, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964; Hanel and John, Reference Hanel and John2014; Villarins et al., Reference Villarins, Dario, Eduardo, Frédou, Bertrand, Prokofiev and Mincarone2022). The species is known from Indian Ocean on the basis of a single record around Seychelles islands (Regan, Reference Regan1908).
Genus Grammatostomias Goode and Bean, 1895
Grammatostomias dentatus Goode and Bean, 1895
IO/SS/FIS/00732, 156 mm, 32116, Figure 1e. First record from Indian waters.
Specimen diagnosis
The specimen was readily identified as Grammatostomias dentatus based on its characteristic line of luminous tissue on sides extending from ends of operculum to anal fin origin (Morrow and Gibbs, Reference Morrow, Gibbs, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964). Counts and measurements of our specimen are summarized in Table 3.
Remarks
This genus is sexually dimorphic, PO is well expressed in males but absent in females (Morrow and Gibbs, Reference Morrow, Gibbs, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964), the absence of PO in our specimen indicates that the fish is a female. This species can be found in all major oceans with maximum reports from the Atlantic (Morrow and Gibbs, Reference Morrow, Gibbs, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964; Moore et al., Reference Moore, Hartel, Craddock and Galbraith2003; Harold, Reference Harold, Carpenter and Angelis2016; Carneiro et al., Reference Carneiro, Martins, Reiner and Batista2019; Villarins et al., Reference Villarins, Dario, Eduardo, Frédou, Bertrand, Prokofiev and Mincarone2022); it is also taken from South-west Pacific (Fricke et al., Reference Fricke, Kulbicki and Wantiez2011). Species is poorly known from Indian Ocean, Harold (Reference Harold, Carpenter and Angelis2016) has reported that the species was distributed in Eastern equatorial Indian Ocean, however it lacked any other information, such as description of specimen and catch locality.
Family Phosichthyidae Weitzman, 1974
Genus Ichthyococcus Bonaparte, 1840
Ichthyococcus parini Mukhacheva, Reference Mukhacheva1981
Total three specimens. Total three specimens. IO/SS/FIS/00572, 31 mm, 344Ι07; IO/SS/FIS/00573, 37 mm, 32008; IO/SS/FIS/00574, 46 mm, 344Ι01, Figure 1f. First record from Indian waters.
Specimen diagnosis
The specimens were diagnosed as Ichthyococcus parini based on an irregular IV photophore row between 8th to 14th IV; interrupted AC row after anal fin ending; inter orbital distance of 6.4–8.3% HL; lateral line scales 37–39; gill raker 21–23 (Mukhacheva, Reference Mukhacheva1981). Counts and measurements of our specimens are summarized in Table 4.
Remarks
This species requires more detailed study as the characters presently used to describe it are difficult to interpret. Except the displaced 8th IV photophore, the rest of the IV appears to be in a straight row unlike an expected curved IV (Mukhacheva, Reference Mukhacheva1981), however a slight curve was observed in our biggest specimen, somewhat similar to the original description (Figure 2 in Mukhacheva, Reference Mukhacheva1981). Ichthyococcus parini's close relative I. irreglaris Rechnitzer and Böhlke, 1958 has a more curved IV photophore row from 8th to 14th IV, further these two species are differentiated on the basis of a broader interorbital distance of 12–12.7% HL and higher gill raker count of 25–28 for the latter species. The interorbital crests converge anterior to eye in I. parini whereas the crests are almost parallel to each other in I. irregularis. There were not many variations in meristic and morphometric characters, except small differences were found in gill raker and lateral line scale counts as well as interorbital distance (Table 4). Mukhacheva (Reference Mukhacheva1981) has given pectoral and pelvic fin base lengths as 22.4–27 and 13–16% SL, respectively; if this is correct, then this species would be having bases that are 0.5–0.8 cm long, which is highly unlikely. We speculate that she must have been referring to lengths of pectoral and ventral fins, with which the latter mentioned length ranges coincide. The species was known only from 13 specimens caught from remote open ocean regions of northern Indian Ocean, including Arabian Sea and Bay of Bengal. However, there are chances that earlier reports of Ichthyococcus ovatus (Cocco, 1838) from Arabian Sea and Bay of Bengal could be misidentifications of I. parini (Mukhacheva, Reference Mukhacheva1981).
Family Sternoptychidae Duméril, 1805
Genus Polyipnus Günther, 1887
Polyipnus limatulus Harold and Wessel, 1998
Total 10 specimens. IO/SS/FIS/00601 (7), 34–44 mm, 32005, Figure 1g; IO/SS/FIS/00602 (3), 43–48 mm, 33101. This is the first record of P. limatulus in the eastern Arabian Sea.
Specimen diagnosis
Our specimens showed all major characters for a species belonging to P. spinosus species complex (Harold, Reference Harold1990), such as the presence of two post temporal spines, Scythe-like ventral preopercular spine, denticulate PV photophore scales all confirm this. Within the complex, the specimens were confirmed as Polyipnus limatulus due to the presence of a discontinuous parietal keel and by the absence of denticles on ACB photophore scales (Harold et al., Reference Harold, Wessel and Jhonson1998). Counts and measurements of our specimens are summarized in Table 4.
Remarks
The species was thought to be endemic to Gulf of Aden and Seas immediately surrounding it (Harold et al., Reference Harold, Wessel and Jhonson1998).
Genus Argyropelecus Cocco, 1829
Argyropelecus sladeni Regan, Reference Regan1908
Total of six specimens. IO/SS/FIS/00588 (2), 45–73 mm, 344ΙΙ02, Figure 1h; IO/SS/FIS/00589, 40 mm, 344Ι09; IO/SS/FIS/00590 (2), 47, 53 mm, 344ΙΙ12; IO/SS/FIS/00591, 73 mm, 344ΙΙ04; IO/SS/FIS/00592 43 mm, 344ΙΙ01. First record from Indian waters.
Specimen diagnosis
The specimens were identified as Argyropelecus sladeni by the presence of two post abdominal spines; SAB, PAN, AN and SC photophores not forming a straight line; presence of a blunt anterior post abdominal spine; dorsal rays nine in number; absence of enlarged canines in lower jaw; a longer upper preopercular spine that extend beyond the preopercular margin; absence of spines below SC (Baird, Reference Baird1971). Counts and measurements of our specimens are summarized in Table 4.
Remarks
The species has a worldwide distribution (Baird, Reference Baird1971) and is also well known from Indian Ocean. The species is reported from eastern Indian Ocean near Australia (Oliver and Beckley, Reference Oliver and Beckley2022), Ninety East Ridge (Timokhin et al., Reference Timokhin, Usachev, Novikov and Rebik2017), Andaman Sea (Satapoomin, Reference Satapoomin2011), from western Indian Ocean (Baird, Reference Baird1971), central Indian Ocean (Bernal et al., Reference Bernal, Toresen and Riera2020) and South West Indian Ocean (Cherel et al., Reference Cherel, Romanov, Annasawmy and Thibault2020; Harris et al., Reference Harris, Noyon, Marsac, Vianello and Roberts2020).
Genus Sternoptyx Hermann, 1781
Sternoptyx obscura Garman, 1899
Total of 40 specimens. IO/SS/FIS/00593 (5), 28–33 mm, 344Ι10; IO/SS/FIS/00594 (2), 23, 25 mm, 344Ι07; IO/SS/FIS/00595 (10), 18–29 mm, 344Ι07, Figure 1i; IO/SS/FIS/00596 (16), 19–33 mm, 344Ι09; IO/SS/FIS/00597 (3), 27–29 mm, 344Ι06; IO/SS/FIS/00598 (3); 28–29 mm, 344Ι08; IO/SS/FIS/00599, 39 mm, 32015. First record from Indian waters.
Specimen diagnosis
The specimens are referred to Sternoptyx obscura based on its longer horizontal extension of the trunk after the AN photophores; by the presence of anal fin pterygiophores that gradually reduces in size; by a dorsal fin base, longer than dorsal blade spine; trunk depth less than trunk length and by the placement of SAN photophore near to AN (Haruta and Kawaguchi, Reference Haruta and Kawaguchi1976; Badcock and Baird, Reference Badcock and Baird1980). Counts and measurements of our specimens are summarized in Table 4.
Remarks
Sternoptyx obscura is primarily an Indo-Pacific species (Badcock and Baird, Reference Badcock and Baird1980; Miya and Nishida, Reference Miya and Nishida1998), however the species seems to have a global distribution as it is reported from South West Atlantic (Villarins et al., Reference Villarins, Dario, Eduardo, Frédou, Bertrand, Prokofiev and Mincarone2022). The species is reported from western Indian Ocean (Baird, Reference Baird1971; Badcock and Baird, Reference Badcock and Baird1980), southern Indian Ocean (Iwami and Kubodera, Reference Iwami and Kubodera1990), eastern Indian Ocean (Baird, Reference Baird1971; Badcock and Baird, Reference Badcock and Baird1980; Timokhin et al., Reference Timokhin, Usachev, Novikov and Rebik2017) and from Andaman Sea (Satapoomin, Reference Satapoomin2011).
Discussion
Mesopelagic fishery resources of Indian EEZ are severely under-surveyed when compared to pelagic habitats, and this shortage of mesopelagic surveys in the EEZ might be the reason why these fishes had been previously unreported from Indian waters. Furthermore, exploratory surveys in these habitats should result in more species being documented. Some differences were visible in barbel morphologies of P. paxtoni, P. barnetti, M. melanops and A. xenostoma (Table 5). Barbel morphology is a crucial identification characteristic for many species in family Stomiidae, but can show much variations. The differences observed in above-mentioned species could have been due to a normal variation associated with region, individual or it also could be regenerating barbel tip. As it is the case for many stomiids, descriptive taxonomic reports are very scarce and often limited to particular areas or oceans. The present study, based on specimens from a different area, improves the taxonomic description, which may often be ambiguous even for well-known species.
Table 5. This list records species identified during the study with voucher numbers, standard lengths, station ids and remarks, new Indian EEZ records not included.
The teeth that are commonly referred to as ‘pterygoid teeth’ by many authors (e.g. Grey, Reference Grey, Biglow, Cohen, Dick, Gibbs, Grey, Morrow, Schultz and Walters1964) were visible on roof of mouth, originating below the orbital region reaching posteriorly (Figure 2). This was observed in many species such as Sigmops, Polyipnus, Margrethia and Vinciguerria. Some sternoptychids also showed signs of such teeth but we were unable to confirm this. Apparently, these are only superficial teeth associated with muscles and tissues on this area and have no connection with actual pterygoid bones of the fish. These teeth are minute and imbedded in the skin inside of the mouth and the entire teeth patch comes along with the skin once stripped. Hence the term pterygoid teeth may be misleading. This might be present in other species of gonostomatids, sternoptychids and phosichthyids but all the stomiids studied by us lacked this feature.
Astronesthes lucifer, Astronesthes niger, Polyipnus spinosus and Vinciguerria lucetia reported from the Indian EEZ (Table 1) are probably misidentifications of some similar species occurring in the area, because, according to recent studies (Jhonson and Feltes, Reference Jhonson and Feltes1984; Harold, Reference Harold1994; Parin and Borodulina, Reference Parin and Borodulina1994, Reference Parin and Borodulina2002), these species are presently not considered to occur in the Indian Ocean. Without doubt these reports demand further validation.
Data Availability
The authors confirm that the data supporting the findings of this study are available within the article.
Acknowledgements
From first author – A huge thanks to Dr Artem Prokofiev (Severtsov Institute of Ecology and Evolution, Moscow, Russia) who has helped me a lot in clearing many of my doubts. I am indebted to Andrew D. Williston and Dr George V. Lauder of the Museum of Comparative Zoology, USA for granting us Diplophos specimens as loan. I am grateful to Dr Ionuţ Grădianu (Natural Science Museum, Romania), Dr Keita Koeda (Kuroshio Biological Research Station, Japan), Cynthia Klepadlo (Scripps Institute of Oceanography) and Amanda Hay (Australian Museum) for helping me understand certain matters related to identification of some species. I wish to thank my friends Albin K. Jose (NIO, Kochi), Vishnu Prasad and Bheemeshwara Rao for their help and support. We extend our gratitude to Dr Bruce Collette (Smithsonian Institution, USA), Yale Peabody Museum press team, Dr Sergei Evseenko (Shirsov Institute of Oceanology, Russia), Dr Catherine Mecklenburg (California Academy of Sciences, USA), Dr Tsuchida San (JAMSTEC), Polly Lasker (Smithsonian Libraries, USA), Andrew Stewart (Museum of New Zealand), for their help in various matters related to the paper.
Financial Support
This study was part of the ongoing Resources Exploration and Inventorization System (REIS) Project of CMLRE funded by the Ministry of Earth Sciences.
Competing Interest
None.
Ethical Standards
Not applicable to this study.
