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All issues Volume 29 (2022) Parasite, 29 (2022) 48 Full HTML
Open Access
Issue
Parasite
Volume 29, 2022
Article Number 48
Number of page(s) 14
DOI https://doi.org/10.1051/parasite/2022049
Published online 25 October 2022

© C. Saengpheng et al., published by EDP Sciences, 2022

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Introduction

Groupers (Serranidae, Epinephelinae) are bottom-associated fishes found in tropical and subtropical seas. Most species occur in coral reefs, but some live in estuaries or on rocky reefs [11]. The Epinephelinae are divided into five tribes that comprise about 234 species of marine fishes in 32 genera [28]. The hybrid grouper, a cross of the female tiger grouper E. fuscoguttatus and the male giant grouper E. lanceolatus (tiger grouper × giant grouper or TGGG), has taken the Asian aquaculture industry by storm since 2006. TGGG is widely cited as the most successful hybrid combination, as it is able to grow quickly [2, 6]. In Thailand, the peacock hind Cephalopholis argus (Bloch & Schneider), the tomato hind C. sonnerati (Valenciennes), the coral hind C. miniata (Forsskål), the giant grouper Epinephelus lanceolatus (Bloch), and the whitespotted grouper E. coeruleopunctatus (Bloch) occur in coral reefs and other coastal and offshore areas; the malabar grouper E. malabaricus (Bloch & Schneider) occurs in mangroves; the cloudy grouper E. erythrurus (Valenciennes) occurs in seagrass beds; and the orange-spotted grouper E. coioides (Hamilton) occurs in both mangroves and seagrass beds [29]. Species of Pseudorhabdosynochus Yamaguti, 1958 are mostly found on the gills of groupers mainly of the genus Epinephelus and appear to be specific to their host [18, 22]. Pseudorhabdosynochus currently has 96 valid species [10]. Four of those species – P. argus Justine, 2007, P. minutus Justine, 2007, P. urceolus Mendoza-Franco, Violante-González & Herrera, 2011, and P. meganmarieae Kritsky, Bakenhaster & Adams, 2015 – have been described from four species of Cephalopholis – C. argus, C. sonnerati, C. panamensis (Steindachner), and C. cruentata (Lacepède) [15, 24, 26], respectively. In this paper, we describe three new species – P. suratthaniensis n. sp. found on the gills of C. argus, P. cephalopholi n. sp. found on the gills of C. sonnerati, and P. samaesarnensis n. sp. found on the gills of E. lanceolatus – in the Gulf of Thailand. Pseudorhabdosynochus argus and P. minutus had earlier been described from C. argus and C. sonnerati off Nouméa, New Caledonia [15], respectively; in this paper, we describe a second species of Pseudorhabdosynochus from these fish. In addition, we describe the first species of Pseudorhabdosynochus from E. lanceolatus: Pseudorhabdosynochus samaesarnensis n. sp.

Materials and methods

One specimen of C. argus (total length, 303 mm and weight, 443 g) was obtained from a jetty in Surat Thani province, Southern Thailand in June 2019. Four specimens of C. sonnerati (total length, 230–247 mm and weight, 234–287 g), and nine specimens of C. miniata (total length, 210–340 mm and weight, 169–637 g) were obtained from a jetty in Surat Thani province, Southern Thailand in May 2019. One specimen of E. lanceolatus (total length, 520 mm and weight, 5000 g) was obtained from a local fisherman on Samaesarn Island in the Gulf of Thailand, Chonburi province, Eastern Thailand in September 2020. Four specimens of E. coeruleopunctatus (total length, 290–330 mm and weight, 378–557 g), four specimens of E. coioides (total length, 350–470 mm and weight, 617–1500 g), five specimens of E. erythrurus (total length, 245–275 mm and weight, 260–338 g), four specimens of E. malabaricus (total length, 360–370 mm and weight, 759–844 g), and eleven specimens of E. fuscoguttatus (total length, 250–350 mm and weight, 270–914 g) were obtained from a local fisherman on Libong Island in the Andaman Sea, Trang province, Southern Thailand in April 2020. Three sea cage-cultured hybrid groupers (TGGG) (E. fuscoguttatus ♀ × E. lanceolatus ♂) (total length, 380–480 mm and weight, 1100–2600 g) were obtained from a local farmer in Ban Laem Hin, Phang-Nga province in the Andaman Sea, Southern Thailand in May 2020. All the fish were dead and were immediately transported in a cool box to the laboratory. Their gills were removed and placed in Petri dishes that contained seawater. Monogeneans were individually picked off the gills with a fine needle with the aid of a stereomicroscope and put on slides. They were prepared with ammonium picrate-glycerin, referred to as “Picrate” (see [13]) according to [25]. Then, their soft internal organs and haptoral hard parts were immediately examined. The slides were later sealed with Canada balsam [13]. Specimens were photographed using an Olympus DP 70 microscope (Olympus Corporation, Japan) and a Zeiss Axiocam 506 color microscope (Carl Zeiss AG, Germany) for drawing. Various sclerotized organs were measured based on a previous study (see Fig. 1 in [13, 14]; their nomenclature follows [14]). Measurements are in μm and given as mean followed by (minimum–maximum, n=) between parentheses. Specimens were deposited in Lee Kong Chian Natural History Museum National University of Singapore (herein abbreviated as ZRC), Natural “”History Museum, National Science Museum, Technopolis, Pathum Thani Province, Thailand (herein abbreviated as THNHM) and Zoological Museum, Kasetsart University (herein abbreviated as ZMKU).

thumbnail Figure 1

Pseudorhabdosynochus suratthaniensis n. sp. from Cephalopholis argus in the lower Gulf of Thailand. (A) COMPOSITE drawing (mainly from holotype), dorsal view. (B) Male quadriloculate organ, dorsal view. (C) Sclerotized vagina, dorsal view. (D) Ventral hamulus. (E) Dorsal hamulus. (F) Ventral bar. (G) Dorsal (lateral) bar. (H) Ventral squamodisc. (I) Dorsal squamodisc. (J) Hooklet. Scale-bars: (A) 200 μm; (B)–(J) 50 μm.

Pseudorhabdosynochus suratthaniensis n. sp.

urn:lsid:zoobank.org:act:69811A09-7C5C-4D38-B2CA-72D77973425C

Type-host: Cephalopholis argus (Bloch & Schneider) (Perciformes, Serranidae).

Type-locality: Surat Thani Province, the lower Gulf of Thailand, Southern Thailand (9°49′10.1″N 99°55′31.1″E), June 2019.

Type-material: Holotype, ZRC.PLA.1115; 2 paratypes, ZRC.PLA.1116-17; 2 paratypes, THNHM-Iv-19363-64; 15 paratypes, ZMKU-PM-002039-53.

Site in host: Gills.

Infection indices: Prevalence 100% (one specimen examined and infected); 36 helminth specimens on the single grouper examined.

Etymology: The species name “suratthaniensis” is treated as an adjective and was derived from the name of the province “Surat Thani”, where the host fish Cephalopholis argus was collected.

Description (Figs. 1 and 2)

[Based on 20 specimens]. Body (including haptor) 759 long (619–977, n = 20); maximum width 169 (121–216, n = 20). Tegument smooth. Anterior region with 3 pairs of lateral head organs and 2 pairs of eye-spots; anterior pair smaller than posterior pair. Pharynx median, spherical, 45 (32–54, n = 20) × 45 (30–54, n = 20). Esophagus absent. Intestinal bifurcation immediately follows pharynx. Haptor differentiated from rest of body, 222 wide (177–277, n = 20), with 2 similar squamodiscs, 2 pairs of lateral hamuli, 3 bars, and 14 marginal hooklets. Dorsal and ventral squamodiscs round-shaped, made up of rows of rodlets, 1–2 central rows oval and closed. Dorsal squamodisc 53 long (41–64, n = 20), 55 wide (40–67, n = 20), with 9–11 rows of rodlets, of which the 1–2 innermost rows form closed ovals. Ventral squamodisc 59 long (47–73, n = 20), 57 wide (41–69, n = 20), with 8–11 rows of rodlets, of which the 1–2 innermost rows form closed ovals. Ventral hamulus with distinct guard and expanded deep root, elongated shaft slightly arched and recurved toward the tip, outer length 49 (44–53, n = 20), inner length 43 (39–47, n = 20). Dorsal hamulus with indistinct guard and expanded deep root, elongated straight shaft and recurved toward the tip, outer length 42 (40–46, n = 20), inner length 27 (25–31, n = 20). Dorsal (lateral) bar straight, with flattened medial extremity and cylindrical lateral extremity, 69 long (56–72, n = 20), 19 wide (16–22, n = 20). Ventral bar 93 long (85–100, n = 20), 18 wide (15–21, n = 20), with constricted median portion, pointed ends and visible groove that extends to both thin extremities. Male quadriloculate organ divided into 4 chambers, inner length 73 (65–84, n = 20), fourth chamber ends in sclerotized cone, 19 long (14–22, n = 20), prolonged by sclerotized tube, 19 long (16–23, n = 20), end of tube prolonged by filament of variable length. Testis subspherical, intercecal. Ovary pretesticular, encircles right intestinal cecum. Vitelline follicles lateral, coextensive with intestinal ceca and confluent in large zone posterior to testis and terminate anterior to peduncle, leaving free space around squamodiscs. Egg not seen.

thumbnail Figure 2

Variations (A)–(F) of the sclerotized vagina of Pseudorhabdosynochus suratthaniensis n. sp. from Cephalopholis argus in the lower Gulf of Thailand. Abbreviations: Tr – trumpet, Ca1 – primary canal, Ch1 – primary chamber, Ca2 – secondary canal. Scale-bar: 50 μm.

Sclerotized vagina with a complex structure, aspect changes slightly according to specimen and orientation (Figs. 2A–2F). Sclerotized vagina comprises anterior trumpet, followed by primary canal, primary chamber and secondary canal; trumpet in continuity with primary canal short, straight, or curved (Figs. 2A and 2D), heavily sclerotized and widens into single large and thick-walled primary chamber; secondary canal connected to primary chamber around base of vagina. Total length of sclerotized vagina (measured from distal extremity of trumpet to base of vagina) 40 (36–45, n = 20), length variable because of variation in curvature of primary canal. Primary chamber subspherical 19 long (15–23, n = 20), 17 wide (16–20, n = 20).

Differential diagnosis

Pseudorhabdosynochus suratthaniensis n. sp. is easily distinguished from other species of Pseudorhabdosynochus by the structure of its sclerotized vagina and the number of rows of rodlets in each of its squamodiscs. Another Pseudorhabdosynochus species that has a vaginal structure similar to that of P. suratthaniensis n. sp. is P. urceolus from C. panamensis from Taboga Island in Panama. The general structure of the sclerotized vagina appeared to be similar to that of the P. suratthaniensis n. sp. Pseudorhabdosynochus urceolus can be distinguished by the following characteristics: the size of its sclerotized vagina (29 versus 40 μm in P. suratthaniensis n. sp.); the morphology of its sclerotized vagina, with a bell-shaped opening that is not in P. suratthaniensis n. sp; and its chamber structure, with a small hollow structure on its margin that is not in P. suratthaniensis n. sp. In addition, the squamodiscs of P. urceolus have numerous rows of rodlets, that is, 14–15 rows of rodlets and a 0–1 innermost row that form complete concentric rings; but the squamodiscs of P. suratthaniensis n. sp. have 8–11 rows of rodlets and 1–2 innermost rows that form closed ovals [26]. Pseudorhabdosynochus bouaini Neifar & Euzet, 2007 from E. costae (Steindachner) out of Sfax, Tunisia has a sclerotized vagina similar to that of P. suratthaniensis n. sp. It is characterized by an anterior trumpet, followed by a short and heavily sclerotized primary canal progressively in the heavy primary chamber. However, the distal part of the primary chamber has two small sclerotized protuberances in P. bouaini (which are not in P. suratthaniensis n. sp) [27].

Pseudorhabdosynochus cephalopholi n. sp.

urn:lsid:zoobank.org:act:FDF79967-ED74-4848-BBA7-DCBC12E813A8

Type host: Cephalopholis sonnerati (Valenciennes) (Perciformes, Serranidae).

Other host: C. miniata (Forsskål) (Perciformes, Serranidae)

Type locality: Surat Thani Province, the lower Gulf of Thailand, Southern Thailand (9°48′10.1″N 99°55′31.1″E), May 2019.

Type-material: Holotype, ZRC.PLA.1118; 2 paratypes, ZRC.PLA.1119-20; 2 paratypes, THNHM-Iv-19365-66; 20 paratypes, ZMKU-PM-002054-73; 2 paratypes from other host, C. miniata, ZMKU-PM-002074-75.

Site in host: Gills.

Infection indices: Prevalence 100% (4/4); mean intensity 62.5 individuals/fish (250/4).

Etymology: Species name derived from Cephalopholis, which is the name of the host genus (both type-host and other host). This monogenean species seems to be specific to this host genus.

Description (Figs. 3 and 4)

[Based on 25 specimens]. Body (including haptor) 393 long (260–645, n = 25), maximum width 106 (83–126, n = 25). Tegument smooth. Anterior region with 3 pairs of lateral head organs and 2 pairs of eye-spots; anterior pair smaller than posterior pair. Pharynx median, spherical, 24 (18–31, n = 25) × 24 (19–31, n = 25). Esophagus absent. Intestinal bifurcation immediately follows pharynx. Haptor differentiated from rest of body, 216 wide (167–261, n = 25), with 2 similar squamodiscs, 2 pairs of lateral hamuli, 3 bars, and 14 marginal hooklets. Dorsal and ventral squamodiscs round-shaped, made up of rows of rodlets; rodlets similar in width in all rows except last row with thin and separate rodlets; central rows form closed ovals. Dorsal squamodisc 39 long (30–56, n = 11), 41 wide (32–57, n = 11), with 8–10 rows of rodlets, the innermost of which form closed oval. Ventral squamodisc 39 long (34–43, n = 11), 43 wide (37–49, n = 11), with 8–10 rows of rodlets, the innermost of which form closed oval. Ventral hamulus with distinct guard and expanded deep root, elongated shaft and recurved toward the tip, outer length 41 (37–46, n = 25), inner length 31 (29–36, n = 25). Dorsal hamulus with indistinct guard and expanded deep root, elongated shaft and recurved toward the tip, outer length 35 (32–38, n = 25), inner length 22 (19–25, n = 25). Dorsal (lateral) bar straight, elongated, with flattened medial extremity and cylindrical lateral extremity, 72 long (64–79, n = 25), 10 wide (7–14, n = 25). Ventral bar flat, thin, elongated, with constricted median portion and pointed ends, 104 long (90–114, n = 25), 10 wide (8–14, n = 25); visible groove that extends to both thin extremities. Male quadriloculate organ divided into 4 chambers, inner length 40 (33–46, n = 25), fourth chamber ends in sclerotized cone, 10 long (7–12, n = 25), lengthened by sclerotized tube, 11 long (6–14, n = 25). Testis subspherical, intercecal. Ovary pretesticular, encircles right intestinal cecum. Vitelline follicles lateral, coextensive with intestinal ceca, confluent posterior to testis region and terminate anterior to peduncle. Egg (Fig. 3D) 86 long (74–91, n = 4), 51 wide (38–64, n = 4).

thumbnail Figure 3

Pseudorhabdosynochus cephalopholi n. sp. from Cephalopholis sonnerati in the lower Gulf of Thailand. (A) Composite drawing (mainly from holotype), dorsal view. (B) Male quadriloculate organ, dorsal view. (C) Sclerotized vagina, dorsal view. (D) Egg. (E) Ventral hamulus. (F) Dorsal hamulus. (G) Dorsal (lateral) bar. (H) Ventral bar. (I) Dorsal squamodisc. (J) Ventral squamodisc. (K) Hooklet. Scale-bars: (A) 100 μm; (B)–(K) 50 μm.
thumbnail Figure 4

Variations (A)–(I) of the sclerotized vagina of Pseudorhabdosynochus cephalopholi n. sp. from Cephalopholis sonnerati in the lower Gulf of Thailand. Abbreviations: Tr – trumpet, Ca1 – primary canal, Ch1 – primary chamber, Ca2 – secondary canal, Ch2 – secondary chamber, As – accessory structure. Scale-bar: 50 μm.

Sclerotized vagina with a complex sclerotized structure, aspect changes according to specimen and orientation (Figs. 4A–4I). Sclerotized vagina comprises anterior trumpet, followed by primary canal, primary chamber, secondary canal, secondary chamber, and accessory structure; trumpet in continuity with primary canal tube, long, coiled (Fig. 4F), or curved (Figs. 4A–E and 4G–4I) at around midlength, heavily sclerotized, progressively into primary chamber or form a bend in posterior region and progressively into primary chamber (Fig. 4H); secondary chamber communicates with primary chamber through a short secondary canal, and accessory structure connected to secondary chamber. Total length of sclerotized vagina (measured from distal extremity of trumpet to base of vagina, not considering curved length along coil or curve of primary canal) 25 (19–30, n = 25), length variable because of variation in coil or curvature of primary canal.

Differential diagnosis

Pseudorhabdosynochus cephalopholi n. sp. is distinguished from other Pseudorhabdosynochus species by the structure of its sclerotized vagina, in addition to the differing lengths of some sclerotized organs and the number of rows of rodlets in each squamodisc. Pseudorhabdosynochus minutus from C. sonnerati out of the Barrier reef off Nouméa, New Caledonia has the following characteristics. The general morphology of its sclerotized vagina and its size (25 μm), body size (270–550 μm versus 260–645 μm in P. cephalopholi n. sp.), number of rows of rodlets in each squamodisc (10–11 rows of rodlets and a 0–1 closed oval), and host species (C. sonnerati) are similar to those of P. cephalopholi n. sp. Pseudorhabdosynochus minutus can be distinguished, however, by the chamber structure of its sclerotized vagina (P. minutus has spherical chambers, unlike the chambers in P. cephalopholi n. sp.). Pseudorhabdosynochus argus from C. argus out of the Barrier reef off Nouméa, New Caledonia has a sclerotized vagina similar to that of P. cephalopholi n. sp., characterized by an anterior trumpet followed by a long primary canal. Pseudorhabdosynochus argus can be distinguished, however, by the size of its sclerotized vagina (38 μm versus 25 μm in P. cephalopholi n. sp.); the morphology of its sclerotized vagina, with the primary canal coiled in its anterior part, just after the trumpet (see [15]), unlike in P. cephalopholi n. sp.; its body size (888 μm versus 393 μm); and the different lengths of its sclerotized organs: of its ventral hamulus, outer length of 53 μm versus 41 μm and inner length of 44 μm versus 31 μm; of its dorsal hamulus, outer length of 44 μm versus 35 μm and inner length of 27 μm versus 22 μm; of its ventral bar, 79 μm long versus 104 μm long; of its quadriloculate organ, inner length of 58 μm versus 40 μm; and of the cone of its quadriloculate organ, 22 μm long versus 10 μm long (Table 1). Pseudorhabdosynochus sp. Justine, 2007 from C. boenak (Bloch) out of Heron Island, Queensland, Australia has a sclerotized vagina similar to that of P. cephalopholi n. sp., characterized by an anterior trumpet followed by a long primary canal. Pseudorhabdosynochus sp. can be distinguished by the following: the morphology of its primary canal, the shapes of its chambers, and the number of rows of rodlets in each of its squamodiscs (7 rows of rodlets, including 0–2 closed rows versus 8–10 rows of rodlets and an innermost row closed oval in P. cephalopholi n. sp.). Pseudorhabdosynochus sp. generally resembles a dwarf P. argus [15]. Pseudorhabdosynochus euitoe Justine, 2007 from E. maculatus (Bloch) out of the Barrier reef off Nouméa, New Caledonia has a sclerotized vagina similar to that of P. cephalopholi n. sp., characterized by an anterior trumpet followed by a long, coiled primary canal. However, the trumpet is characterized by a heavily sclerotized ring at the trumpet-canal limit in the P. euitoe (which is absent in P. cephalopholi n. sp.). Pseudorhabdosynochus fuitoe Justine, 2007 from E. maculatus out of the Barrier reef off Nouméa, New Caledonia has a sclerotized vagina similar to that of P. cephalopholi n. sp., characterized by an anterior trumpet followed by a heavy, long, coiled or curved primary canal, but the shapes of their chambers differ [14]. Pseudorhabdosynochus manifestus Justine & Sigura, 2007 from E. malabaricus (Bloch & Schneider) out of the Lagoon off Nouméa, New Caledonia is differentiated by its sclerotized vagina and its cone-shaped primary canal that is coiled in its anterior part and straight in its posterior part (which is absent in P. cephalopholi n. sp.) [20].

Table 1

Measurements of P. cephalopholi n. sp. from the type host, C. sonnerati, C. miniata, and two previously described Pseudorhabdosynochus species from Cephalopholis spp. The measurements of P. cephalopholi n. sp. were taken from flattened specimens in ammonium picrate-glycerin.

Pseudorhabdosynochus samaesarnensis n. sp.

urn:lsid:zoobank.org:act:EF09975F-D751-41C5-B742-154A1B5E48FE

Type host: Epinephelus lanceolatus (Bloch) (Perciformes, Serranidae).

Other hosts: E. coioides (Hamilton), E. erythrurus (Valenciennes), E. coeruleopunctatus (Bloch), E. malabaricus (Bloch & Schneider), sea cage-cultured hybrid grouper (TGGG) (E. fuscoguttatus ♀ × E. lanceolatus ♂) and E. fuscoguttatus (Forsskål) (Perciformes, Serranidae).

Type-locality: Samaesarn Island in the Gulf of Thailand, Chonburi Province, Eastern Thailand (12°34′30.9″N 100°57′33.7″E), September 2020.

Other locality: Libong Island in the Andaman Sea, Trang Province, Southern Thailand (7°13′00.3″N 99°21′36.0″E), April 2020; Ban Laem Hin, Phang-Nga Province in the Andaman Sea, Southern Thailand (8°10′55.5″N 98°20′35.3″E), May 2020.

Type-material: Holotype, ZRC.PLA.2041; 2 paratypes, ZRC.PLA.2042-43; 2 paratypes, THNHM-Iv-19367-68; 1 paratype, ZMKU-PM-002076; 2 paratypes from other host, E. coioides, ZMKU-PM-002077-78; 2 paratypes from other host, E. erythrurus, ZMKU-PM-002079-80; 2 paratypes from other host, E. coeruleopunctatus, ZMKU-PM-002081-82; 2 paratypes from other host, E. malabaricus, ZMKU-PM-002083-84; 1 paratype from other host, sea cage-cultured hybrid grouper (TGGG) (E. fuscoguttatus ♀ × E. lanceolatus ♂), ZMKU-PM-002085.

Site in host: Gills.

Infection indices: Prevalence 100% (one specimen examined and infected); 12 helminth specimens on the single grouper examined.

Etymology: The species name “samaesarnensis” was derived from “Samaesarn Island”, where the host fish Epinephelus lanceolatus was collected.

Description (Figs. 5 and 6)

[Based on 6 specimens]. Body (including haptor) 745 long (679–821, n = 6); maximum width 198 (160–234, n = 6). Tegument scaly (observed in some specimens). Anterior region with 3 pairs of lateral head organs and 2 pairs of eye-spots; anterior pair smaller than posterior pair. Pharynx median, spherical, 45 (39–47, n = 6) × 45 (39–47, n = 6). Esophagus absent. Intestinal bifurcation immediately follows pharynx. Haptor differentiated from rest of body, 220 wide (178–243, n = 6), with 2 similar squamodiscs, 2 pairs of lateral hamuli, 3 bars, and 14 marginal hooklets. Squamodiscs round-shaped, made up of rows of rodlets, the innermost 1–2 rows of which form closed ovals and last row of which are thinner and separated. Dorsal squamodisc 53 long (51–54, n = 4), 47 wide (44–50, n = 4), with 9–12 rows of rodlets, the innermost 1–2 rows of which form closed ovals. Ventral squamodisc 52 long (49–56, n = 4), 45 wide (41–52, n = 4), with 9–10 rows of rodlets, the innermost 1–2 rows of which form closed ovals. Ventral hamulus with distinct guard and expanded deep root, elongated shaft slightly arched and recurved toward the tip, outer length 48 (45–51, n = 6), inner length 37 (35–39, n = 6). Dorsal hamulus with indistinct guard and expanded deep root, elongated shaft slightly arched and recurved toward the tip, outer length 41 (40–41, n = 6), inner length 25 (24–27, n = 6). Dorsal (lateral) bar straight, with flattened medial extremity, 61 long (57–67, n = 6), 17 wide (16–19, n = 6). Ventral bar elongated, with constricted median portion and tapered ends, 94 long (92–96, n = 6), 15 wide (14–16, n = 6); visible groove that extends to both thin extremities. Male quadriloculate organ with fourth (posterior) chamber slightly more sclerotized than 3 anterior chambers, inner length 56 (51–60, n = 6), fourth chamber ends in sclerotized cone, 12 long (10–13, n = 6), prolonged by sclerotized tube, 15 long (13–17, n = 6), end of tube prolonged by filament of variable length. Test is subspherical, intercecal. Ovary pretesticular, encircles right intestinal cecum. Vitelline follicles lateral, coextensive with intestinal ceca and terminate anterior to the peduncle. Egg not seen.

thumbnail Figure 5

Pseudorhabdosynochus samaesarnensis n. sp. from Epinephelus lanceolatus from Samaesarn Island in the Gulf of Thailand. (A) Composite drawing (mainly from holotype), dorsal view. (B) Male quadriloculate organ, dorsal view. (C) Sclerotized vagina, dorsal view. (D) Ventral hamulus. (E) Dorsal hamulus. (F) Dorsal (lateral) bar. (G) Ventral bar. (H) Dorsal squamodisc. (I) Ventral squamodisc. (J) Hooklet. Scale-bars: (A) 200 μm. (B)–(J): 50 μm.
thumbnail Figure 6

Variations (A)–(F) of the sclerotized vagina of Pseudorhabdosynochus samaesarnensis n. sp. from Epinephelus lanceolatus and E. coioides in the Gulf of Thailand. Abbreviations: Tr – trumpet, Ca1 – primary canal, Ch1 – primary chamber. As, accessory structure. Scale-bar: 50 μm.

Sclerotized vagina with a complex sclerotized structure, aspect changes according to specimen and orientation (Figs. 6A–6F). Sclerotized vagina comprises anterior cup-shaped trumpet, followed by primary canal, primary chamber and accessory structure; thick-walled anterior cup-shaped trumpet in continuity with short straight or curved primary canal (Fig. 6A), thick-walled sclerotization and widens into a thick-walled primary chamber; accessory structure connects to the primary chamber. Total length of sclerotized vagina (measured from distal extremity of trumpet to base of vagina, not considering curve along primary canal) 27 (25–29, n = 6), length variable because of variation in curvature of primary canal.

Differential diagnosis

Pseudorhabdosynochus samaesarnensis n. sp. is distinguished from other Pseudorhabdosynochus species by the structure of its sclerotized vagina. Pseudorhabdosynochus samaesarnensis n. sp. has a vaginal structure similar to that of P. nhatrangensis from E. coioides (Hamilton) and E. bleekeri (Vaillant) off Vietnam. The structure of their sclerotized vagina was found to be very similar, but the number of rows of rodlets found in P. nhatrangensis was always 10 [7], while in P. samaesarnensis n. sp., the rows were found to vary in number from 9 to 13. In addition, the specimens of P. samaesarnensis n. sp. from E. lanceolatus were larger than those of P. nhatrangensis from E. coioides and E. bleekeri (Table 2). However, P. nhatrangensis Dang, Bristow, Schander & Berland, 2013 is not a valid species because the article was not compliant with the new Article 8.5.3 of the International Code of Zoological Nomenclature (ICZN) [3].

Table 2

Measurements of specimens of P. samaesarnensis n. sp. from the type host, E. lanceolatus from the Gulf of Thailand, compared with P. nhatrangensis from E. coioides and E. bleekeri from Nha Trang Bay, Vietnam.

Discussion

Species of Pseudorhabdosynochus parasitize marine fish, especially groupers (Serranidae, Epinephelinae) [3, 5, 21, 24, 33], and have hitherto been considered strictly host-specific or “specialists,” that is, found in a single species [12–16, 20, 22, 33]. However, other Pseudorhabdosynochus species occur on several host species, such as P. cyanopodus Sigura & Justine, 2008 on E. cyanopodus (Richardson) and E. chlorostigma (Valenciennes) [19, 33, 36]; P. amplidiscatum (Bravo-Hollis, 1954) Kritsky & Beverley Burton, 1986 on E. analogus (Gill) and E. labriformis (Jenyns); P. guerreroensis Mendoza-Franco, Violante-González & Herrera, 2011 on Alphestes immaculatus (Breder), A. multiguttatus (Günther) and E. analogus [26]; P. huitoe Justine, 2007 on E. maculatus and E. cyanopodus [14, 33]; P. firmicoleatus Kritsky, Bakenhaster & Adams, 2015 on Hyporthodus flavolimbatus (Poey) and H. niveatus (Valenciennes); and P. sulamericanus Santos, Buchmann & Gibson, 2000 on H. niveatus, H. nigritus (Holbrook), and H. haifensis (Ben-Tuvia) [4, 24, 34]. The sclerotized vaginae are characteristic of individual species and are important for species identification [5, 12–14, 17, 21, 23, 26, 31–33].

Three new species of Pseudorhabdosynochus are described. Pseudorhabdosynochus suratthaniensis n. sp. was found on a single host species, C. argus, while P. cephalopholi n. sp. and P. samaesarnensis n. sp. were found on two host species and seven host species, respectively. Pseudorhabdosynochus cephalopholi n. sp. was found on C. sonnerati and C. miniata, and its morphometric data from both C. sonnerati and C. miniata are similar in size (Table 1). In addition, the structures of the sclerotized vaginae are no different (P. cephalopholi n. sp., which is rare in C. miniata). Pseudorhabdosynochus samaesarnensis n. sp. was found on seven host species: E. lanceolatus, E. coioides, E. erythrurus, E. coeruleopunctatus, E. malabaricus, sea cage-cultured hybrid grouper (TGGG) (E. fuscoguttatus ♀ × E. lanceolatus ♂), and E. fuscoguttatus, and the morphometric data of P. samaesarnensis n. sp. from the six hosts are similar in size (Table 3). In addition, the structures of the sclerotized vaginae are no different. This table does not include the details of P. samaesarnensis n. sp. from E. fuscoguttatus because its specimens are incomplete and are found in low numbers (prevalence: about 9.1%). Pseudorhabdosynochus samaesarnensis n. sp. has a structure of the sclerotized vagina different from other species previously found in host fish – E. coioides [1, 9, 37–39], E. erythrurus [30], E. coeruleopunctatus [35], E. malabaricus [20], and sea cage-cultured hybrid grouper (TGGG) (E. fuscoguttatus ♀ × E. lanceolatus ♂) [8]. We hypothesized that P. cephalopholi n. sp. and P. samaesarnensis n. sp. have low specificity to their hosts and that their infestations of more than one congeneric host species help to perpetuate this parasitic species [36].

Table 3

Measurements of P. samaesarnensis n. sp. from the type host, E. lanceolatus and its other hosts, E. coioides, E. erythrurus, E. coeruleopunctatus, E. malabaricus, and sea cage-cultured hybrid grouper (TGGG) (E. fuscoguttatus ♀ × E. lanceolatus ♂).

Conflict of interest

The authors declare that they have no conflict of interest in relation to this article.

Acknowledgments

This work was supported by International SciKU Branding (ISB), Faculty of Science, Kasetsart University, Graduate Scholarships from the Faculty of Science, Kasetsart University, and the Department of Zoology, Faculty of Science, Kasetsart University, Bangkok, Thailand. The authors would like to express our gratitude to those who helped us find specimens of giant grouper Epinephelus lanceolatus, and we would like to thank the Department of Zoology, Faculty of Science, Kasetsart University, Bangkok, Thailand, for the use of their laboratory facilities. This research was approved by the Institutional Animal Care and Use Committee, Faculty of Science, Kasetsart University, Thailand under project number ACKU61-SCI-032.

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Cite this article as: Saengpheng C & Purivirojkul W. 2022. Three new species of Pseudorhabdosynochus (Monogenea, Diplectanidae) from several species of Cephalopholis and Epinephelus (Perciformes, Serranidae) from Thailand. Parasite 29, 48.

All Tables

Table 1

Measurements of P. cephalopholi n. sp. from the type host, C. sonnerati, C. miniata, and two previously described Pseudorhabdosynochus species from Cephalopholis spp. The measurements of P. cephalopholi n. sp. were taken from flattened specimens in ammonium picrate-glycerin.

In the text
Table 2

Measurements of specimens of P. samaesarnensis n. sp. from the type host, E. lanceolatus from the Gulf of Thailand, compared with P. nhatrangensis from E. coioides and E. bleekeri from Nha Trang Bay, Vietnam.

In the text
Table 3

Measurements of P. samaesarnensis n. sp. from the type host, E. lanceolatus and its other hosts, E. coioides, E. erythrurus, E. coeruleopunctatus, E. malabaricus, and sea cage-cultured hybrid grouper (TGGG) (E. fuscoguttatus ♀ × E. lanceolatus ♂).

In the text

All Figures

thumbnail Figure 1

Pseudorhabdosynochus suratthaniensis n. sp. from Cephalopholis argus in the lower Gulf of Thailand. (A) COMPOSITE drawing (mainly from holotype), dorsal view. (B) Male quadriloculate organ, dorsal view. (C) Sclerotized vagina, dorsal view. (D) Ventral hamulus. (E) Dorsal hamulus. (F) Ventral bar. (G) Dorsal (lateral) bar. (H) Ventral squamodisc. (I) Dorsal squamodisc. (J) Hooklet. Scale-bars: (A) 200 μm; (B)–(J) 50 μm.
In the text
thumbnail Figure 2

Variations (A)–(F) of the sclerotized vagina of Pseudorhabdosynochus suratthaniensis n. sp. from Cephalopholis argus in the lower Gulf of Thailand. Abbreviations: Tr – trumpet, Ca1 – primary canal, Ch1 – primary chamber, Ca2 – secondary canal. Scale-bar: 50 μm.
In the text
thumbnail Figure 3

Pseudorhabdosynochus cephalopholi n. sp. from Cephalopholis sonnerati in the lower Gulf of Thailand. (A) Composite drawing (mainly from holotype), dorsal view. (B) Male quadriloculate organ, dorsal view. (C) Sclerotized vagina, dorsal view. (D) Egg. (E) Ventral hamulus. (F) Dorsal hamulus. (G) Dorsal (lateral) bar. (H) Ventral bar. (I) Dorsal squamodisc. (J) Ventral squamodisc. (K) Hooklet. Scale-bars: (A) 100 μm; (B)–(K) 50 μm.
In the text
thumbnail Figure 4

Variations (A)–(I) of the sclerotized vagina of Pseudorhabdosynochus cephalopholi n. sp. from Cephalopholis sonnerati in the lower Gulf of Thailand. Abbreviations: Tr – trumpet, Ca1 – primary canal, Ch1 – primary chamber, Ca2 – secondary canal, Ch2 – secondary chamber, As – accessory structure. Scale-bar: 50 μm.
In the text
thumbnail Figure 5

Pseudorhabdosynochus samaesarnensis n. sp. from Epinephelus lanceolatus from Samaesarn Island in the Gulf of Thailand. (A) Composite drawing (mainly from holotype), dorsal view. (B) Male quadriloculate organ, dorsal view. (C) Sclerotized vagina, dorsal view. (D) Ventral hamulus. (E) Dorsal hamulus. (F) Dorsal (lateral) bar. (G) Ventral bar. (H) Dorsal squamodisc. (I) Ventral squamodisc. (J) Hooklet. Scale-bars: (A) 200 μm. (B)–(J): 50 μm.
In the text
thumbnail Figure 6

Variations (A)–(F) of the sclerotized vagina of Pseudorhabdosynochus samaesarnensis n. sp. from Epinephelus lanceolatus and E. coioides in the Gulf of Thailand. Abbreviations: Tr – trumpet, Ca1 – primary canal, Ch1 – primary chamber. As, accessory structure. Scale-bar: 50 μm.
In the text

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