Nerocila species (Crustacea, Isopoda, Cymothoidae) from Indian marine fishes

Eleven Nerocila species are recorded from 22 marine fishes belonging to 15 families. Three, Nerocila arres, Nerocila depressa, and Nerocila loveni, are new for the Indian fauna. N. arres and Nerocila sigani, previously synonymized, are redescribed and their individuality is restored. Nerocila exocoeti, until now inadequately identified, is described and distinctly characterized. A neotype is designated. New hosts were identified for N. depressa, N. loveni, Nerocila phaiopleura, Nerocila serra, and Nerocila sundaica. Host–parasite relationships were considered. The parasitologic indexes were calculated. The site of attachment of the parasites on their hosts was also observed. A checklist of the nominal Nerocila species until now reported from Indian marine fishes was compiled.


Introduction
Many fish species are parasitized by Cymothoid isopods. They are found from various parts of the fish, on the skin, on the fins, in the buccal or branchial cavities, sometimes in a pouch. Some are highly host specific, even in the manca stage (Trilles 1964;Tsai et al. 1999). However, several species show a poor host specificity and the mancae may attach and feed on optional intermediate hosts belonging to different fish families (Sarusic 1999) and sometimes even on several other organisms (Trilles and Öktener 2004;Wunderlich et al. 2011).
Until now few studies were performed on parasites collected from Indian marine fishes (Pillai , 1964Ravichandran et al. 2010;Rameshkumar et al. 2011Rameshkumar et al. , 2012aTrilles et al. 2011). Nevertheless, 17 nominal species belonging to the genus Nerocila were so far reported from India. However, several of these reports, often published in local journals not easily accessible, contain misidentifications and descriptions that are of doubtful validity. Thus, a more accurate study of the Indian Nerocila species is necessary .
In the present survey, 11 species were collected. Parasitologic indexes, host species, and geographic distribution are reported for each. A taxonomic study is performed for N. arres, Nerocila exocoeti, and Nerocila sigani, poorly known or inadequately identified. A comprehensive summary of the nominal Nerocila species until now recorded from India is also provided.

Materials and methods
One thousand six hundred forty-six specimens belonging to 22 fish species were directly collected from the trawlers Electronic supplementary material The online version of this article (doi:10.1007/s00436-012-3263-5) contains supplementary material, which is available to authorized users. landed at the Tamil Nadu coasts in South India ( Fig. 1 and Table 1) from April 2009 to December 2011. Samplings were performed twice monthly. Isopods were removed alive from the host and immediately placed into 70 % ethanol. The sampling date, locality, host fish, and site of attachment on the host fish were recorded. Mouthparts and appendages were carefully dissected using dissecting needles and forceps. Drawings were made with the aid of a camera lucida. The total length of isopods was measured and recorded in millimeters. The overall prevalence (number of infested hosts/number of examined hosts×100 %) and intensity (total number of parasites/number of infested hosts) were calculated according to Margolis et al. (1982) and Bush et al. (1997) as well as the mean prevalence and intensity for each parasite-host association. The parasites were identified according to ), Trilles, (19751979), Bowman (1978, Bowman and Tareen (1983), Bruce (1987a), Bruce and Harrison-Nelson 1988), and Rameshkumar et al. (2011). Voucher specimens were deposited at the Annamalai University, India (collection Ravichandran) and at the National Museum of Natural History, Paris, France (Appendix). Host nomenclature and fish taxonomy are according to Fish Base (Froese and Pauly 2011). A checklist of the Nerocila nominal species already reported from Indian marine fishes, updated with our new reports, was compiled (Electronic supplementary material).
However, the validity of N. arres, N. exocoeti, and N. sigani, was still to be verified.
Antenna with nine articles, 1-2 larger than 3-9, article 4 with two plumose setae, 8-9 with four spiny setae. Mandibular palp article 1 largest, with seven irregular smoothly rounded setae at apex of third article. Maxillula with three terminal spines. Maxilla with two spines on medial lobe and one spine on lateral lobe. Maxilliped with oostegial lobe, distal palp segment with five spines. Pereopods 1-5 without marginal hooked spines, pereopod 6 with one spine on merus, four spines on carpus, and five spines on propodus, pereopod 7 with two rows of three and 5 spines respectively on merus, two rows of three and four spines on carpus and a row of seven spines on propodus. Dactyls of pereopods 1, 2, 4, and 5 with distinct swellings. Pleopods 1-2 with five coupling hooks on protopod medial margin; pleopod 2 with appendix masculina about 0. 5 length of endopod; endopod 1-5 with proximomedial lobe well developed, 1-2 not folded, 3-5 folded; endopod 3-4 with few folds, pleopod 5 endopod with several large folds. Exopod of uropod longer than endopod; endopod not extending, or slightly, beyond posterior margin of pleotelson, with very deep notch on medial margin and serrate lateral margin with a row of 15-16 dissimilar teeth.
Antennula distinctly thicker than antenna, 8 articled, articles 5-8 each with posterodistal cluster of esthetes; antenna, 10 articled, 7-10 with setae. Mandible palp article 1 largest and article 3 without setae on distolateral margin; maxillula with three terminal spines; maxilla with two spines on medial lobe and one spine on lateral lobe; maxilliped with oostegial lobe, distal palp segment with three terminal spines. All pereopods without marginal spines, dactylus longer than propodus; pleopods 1-2 with all rami lamellar, three or four couplings hooks on protopod medial margin of pleopod 1 only, endopod proximomedial lobe well-developed but not folded; pleopod 2 with appendix masculina about 0.5 length of endopod; pleopods 3-4 endopod with a single or double lobe, proximomedial lobe well-developed and folded; pleopod 5 endopod with several large folds and proximomedial lobe well-developed and folded. Uropod slender, tapering and sublinear exopod and endopod, exopod about two times longer than endopod; endopod reaching or extending scarcely beyond the posterior margin of pleotelson; exopod extending by far beyond it.
As already reported by , the entire body of the specimens was steel blue in color, with many chromatophores.
For some species, the host-isopod association was not very specific. N. phaiopleura was collected from 13 host species belonging to seven families and 11 genera.and N. sundaica from six host species belonging to five families and six genera. These two species show a euryxenic parasitic specificity. While N. exocoeti and N. trichiura, only collected from the flying fish E. volitans, and N. sigani, only collected on the rabbit fish Siganus oramin, show an oïoxenic parasitic specificity. Carangoides malabaricus, E. volitans, Leiognathus splendens, Otolithes ruber, Sardinella gibbosa, Selaroides leptolepis, Terapon puta, and Thryssa mystax were parasitized by at least two species of Nerocila. Fifteen new hosts were identified, seven for N. phaiopleura, four for N. sundaica, and one for N. depressa, N. exocoeti, N. loveni, and N. serra (Table 1).
Four species, N. arres, N. loveni, N. serra, and N. sigani, were attached on the caudal peduncle or on the caudal fin of the fishes. N. depressa, N. exocoeti, N. longispina, N. phaeopleura, N. poruvae, N. sundaica, and N. trichiura, were collected from the body surface, on the head, on the pectoral fin or from the caudal peduncle of hosts.

Discussion
In the present study, 11 Nerocila species were collected and N. arres, N. exocoeti, and N. sigani were redescribed.
N. arres and N. sigani were described by Bowman and Tareen (1983). They were collected on Nemipterus japonicus, Nemipterus tolu, Epinephelus tauvina, Acanthopagrus latus (N. arres; Holotype from N. japonicus), and Siganus oramin (N. sigani; Holotype from S. oramin) from Kuwait (Arabian Gulf). These two species were accepted as valid by Bruce (1987a) and Trilles (1994). However, they were synonymized by Bruce and Harrisson-Nelson (1988). These authors stated that N. sigani is the senior synonym to N. arres, but without an examination of specimens from the host fishes recorded by Bowman and Tareen (1983). Indeed, the material examined Fig. 8 a-m N. exocoeti Pillai 1954, ovigerous female (MNHN-IU-2009-1936: a mandible; b maxillule; c maxilla; d maxilla, apex; e maxilliped; f maxilliped article 3; g-m, pereopods 1-7 by Bruce and Harrisson-Nelson was collected on Sciaenia dussumieri, Argyrosoma hololepidotus, Argyrosoma macrocephalus, Argyrosoma nibe, Parastromateus niger, and Pomadasys sp. Thus, it was interesting to benefit from our material to verify the validity of the species N. arres and N. sigani. We redescribed here in detail the specimens that we collected respectively from the type hosts N. japonicus and S. oramin, including the mouthparts not examined by Bowman and Tareen (1983) and Bruce and Harrisson-Nelson (1988). Our results reveal that the synonymy of these two species cannot be maintained. Indeed, N. sigani and N. arres can be distinguished mainly by: cephalon as wide as long (N. sigani) or 0.75 as long as wide (N. arres); antennulae more separated at base in N. sigani; posteroventral corners of all pereonites shaped into points and coxae with pointed processes longer, narrower, and more acute in N. sigani than in N. arres; pleotelson smoothly rounded (N. sigani) or with lateral margins curving to medial point (N. arres); pereopods without distinct swellings in dactyls (N. sigani) or with distinct dactylus nodules in P1, P2, P4, and P5 (N. arres); posterior margin of pleonites 1 and 2 longer, narrower, and more acute in N. sigani than in N. arres; uropod serrations on the lateral margin of endopod distinct, with 10 regular teeth in N. sigani and 15-16 dissimilar teeth in N. arres; maxilla with five spines on medial lobe and one spine on lateral lobe (N. sigani) or two spines on median lobe and one spine on lateral lobe (N. arres); mandible palp article 3 with three setae on the distolateral margin (N. sigani) or seven setae (N. arres). Our drawings does not match the illustrations produced by Bruce and Harrisson-Nelson (1988) for two specimens, one collected from an unknown Malaysian host (USNM 232015) and another found on Argyrosoma nibe from Taiwan (USNM 232017), certainly not belonging to N. arres and N. sigani. Some drawings from Bowman and Tareen (1983) for two specimens collected respectively from A. latus and E. tauvina does not correspond to N. arres.
N. exocoeti was identified by  from a large number of specimens in all stages of development collected on Parexocoetus brachypterus from Travancore, India. However, no figures have been published. The author specified only that the main distinguishing character of this species is the comparative size of the coxal plates, the second being small, not extending beyond the posterior border of the segment and the seventh reaching the tip of the first pleon segment, and that the entire body is steel blue in color. Males were collected but not described by . N. exocoeti was later collected on P. brachypterus and Scomberomorus multiradiatus (gut contents?) from Papua New Guinea, Indonesia, and Taiwan by Bruce and Harrisson-Nelson 1988). Figures of one specimen (photos of the dorsal and ventral view) collected on the flying fish E. volitans from the Parangipettai Coast, South-East coast of India, were recently published (Sivasubramanian et al. 2011). N. exocoeti remained a poorly known species. A detailed redescription of this species was necessary.
Until now, two Nerocila species, N. exocoeti and N. trichiura (Miers 1877) were collected from fishes belonging to Fig. 9 a-e N. exocoeti , ovigerous female (MNHN-IU-2009-1936: a-e, pleopods 1-5 the family Exocoetidae. Due to some marked differences, these two species are readily distinguishable. Indeed, in N. trichiura (Fig. 7j), the anterior margin of the cephalon is subtruncate, the posterior angle of pereonite 7 does not extend posteriorly in an acute process, the coxae 2-7 are produced into a rounded process, the ventrolateral margins of pleonites 1-2 are distinctly shorter than in N. exocoeti; the uropods are much longer, exopod and endopod extending far beyond the distal margin of pleotelson; the live specimens are whitish (Fig. 2k).
While the holotype of N. trichiura is held at the British Museum (Natural History) (Holotype: 1846: 104. Mauritius. Presented by Robert Templeton), the Pillai's Indian specimens of N. exocoeti are not extant. Thus, the specimen MNHN-IU-2009-1937 is designate here as neotype of N. exocoeti.
Until now, 17 Nerocila nominal species and four parasites not yet identified to the species level were recorded from India (Electronic supplementary material). The validity of several of them is still to be verified. Nerocila madrasensis was poorly described by Ramakrishna and Venkata Ramaniah (1978) who suggested that this species resembles to N. serra and N. trichiura. Possibly related to N. trichiura according to Bruce (1987a), N. madrasensis and N. trichiura were provisionally synonymized by Trilles (1994) and Trilles et al. (2011). Nerocila pigmentata was synonymized with N. depressa by Trilles (1975Trilles ( ), 1994, Bruce and Harrison-Nelson (1988) and Trilles et al. (2011) but it will be useful to verify once more this synonymy. Besides that, the species identified by Parimala (1984) as N. pigmentata is of uncertain identity and clearly not N. depressa (Bruce and Harrisson-Nelson 1988). Nerocila priacanthusi, resembles to N. serra according to Kumari et al. (1987). However, since the endopod of uropod of this species is with deep notchs on lateral margin as figured by the authors, this species is really similar to N. arres. This species is maybe a junior synonym of N. arres . Nerocila pulicatensis was not reported since its original description by Jayadev Babu and Sanjeeva Raj (1984). Possibly related to Nerocila latiuscula, the description provided by the authors precludes for the moment assessment of the status of this species. Nerocila recurvispina was also not reported since its original description by Schioedte and Meinert (1881) from a single specimen collected at Calcutta on an unknown fish host. Additional specimens are required to describe this species according to modern standards or to verify if it remains a valid species. Nerocila trivittata is maybe the senior synonym of N. serra (Trilles 1979). However, Bowman and Tareen (1983) suggested that the question of the identity of N. trivittata and N. serra cannot be resolved now because the type of N. trivittata is not extant.