Introduction

The spectrum of helminth parasites of freshwater piscine hosts has been scantily studied and there is limited information available on this aspect pertaining to the northeastern region of India. In context of Meghalaya there are very few reports available on the parasitic helminth fauna of fishes, wherein the occurrence of some trematode species has been recorded (Srivastava and Ghosh 1967; Soota and Ghosh 1977); however the caryophyllidean cestode fauna of siluriform fishes is relatively well documented (Chakravarty and Tandon 1988; Tandon et al. 2005).

During an exploratory survey of edible freshwater fishes in Meghalaya, a wide spectrum of Cypriniformes, Channiformes and Siluriformes fish species were examined for the platyhelminth fauna sustained by them. Of the fishes examined, the species of Labeo (Cypriniformes) and Mystus (Siluriformes) were found to harbor two monogenean fluke species. In the present communication we redescribe these species, the occurrence of which is being reported for the first time from the northeastern region of India.

Materials and methods

A large number of specimens of Bifurcohaptor indicus were recovered from the gills of the catfish Mystus tengara and M. vittatus and 45 specimens of Diplozoon cauveri were collected from the gill filaments of 42 Labeo pangusia and 8 specimens from 6 Labeo boga. The recovered parasites were flattened, fixed in 70% alcohol and processed for wholemount preparations following standard procedure and using Borax carmine and Mayer’s carmalum as stains. For scanning electron microscopy (SEM) the specimens fixed in 4% cold neutral buffered formalin were processed and treated with tetramethylsilane (Roy and Tandon, 1991), metal coated and viewed under a LEO 435 VP scanning electron microscope at accelerating electron voltage ranging between 10–20 kV. Measurements of the body and the various structures are given in millimeters.

Results

Monopisthocotylea

  • Order: Dactylogyridea Bychowsky, 1937

  • Family: Dactylogyridae Bychowsky, 1933

  • Genus: Bifurcohaptor Jain, 1958

  • Bifurcohaptor indicus Jain, 1958 (Figs. 1, 2).

    Fig. 1
    figure 1

    Bifurcohaptor indicus: a Whole worm; b opisthaptor enlarged showing (i) entire haptor with its armature, (ii) ventral anchors, (iii) ventral bars, (iv) dorsal bar; and c male copulatory complex showing accessory piece and copulatory tube

    Full size image
    Fig. 2
    figure 2

    SEM of Bifurcohaptor indicus: a Whole worm (scale bar 100 μm); b posterior end showing the two haptors (scale bar 50 μm); c magnified dorsal anchor showing recurved hooks (scale bar 10 μm); and d dorsal bar in higher magnification (scale bar 10 μm)

    Full size image

Body elongated, blunt anteriorly. Cephalic region broad, head organs paired, with a set of four organs lying on either lateral side of anterior end. Eye spots two pairs, posterior pair larger than anterior. Opisthaptor forceps-like, deeply bifurcated, nearly 1/3rd of total body length; armature of opisthaptor comprising two pairs of anchors, larger dorsal and smaller ventral; each dorsal anchor with three sclerotized plates—one median, two dorsolateral, anchor comprising a stout base, long shaft and strong recurved points; ventral anchors very small, lying at extremities of haptor, each with bifurcate base, shaft and fine recurved point, ventral bars two. Pharynx oval; oesophagus short; intestinal ceaca bifurcated, united just anterior to haptor. Testis and ovary single; male copulatory complex consisting of copulatory tube and single accessory piece. Vitellaria follicular, densely spread throughout body except at region of reproductive organs. Eggs not observed. SEM observations revealed the presence of smooth body surface, devoid of any spines or papillate structures. Measurements of the body are provided in Table 1.

Table 1 Observations on Bifurcohaptor indicus Jain, 1958
Full size table

  • Host—Mystus tengara, M. vittatus

  • Location—Gill filaments

  • Locality—Dawki, Byrnihat (Meghalaya).

Remarks

The genus Bifurcohaptor was erected by Jain (1958) with B. indicus as its type species, from gill filaments of Mystus vittatus at Lucknow. The genus Bagaritrema, described by Tripathi (1959) from gill filament of Bagarius bagarius, is a synonym of Bifurcohaptor (Yamaguti, 1963). Species of Bifurcohaptor so far reported from India include: B. indicus Jain, 1958 from Mystus vittatus; B. giganticus Jain, 1958 (= Bagaritrema son Tripathi, 1959) from M. seengala (= Sperata seengala); B. minutum Kulkarni, 1969 from M. tengara; B. vishwanathai Agarwal and Kumar, 1977 from Bagarius bagarius; B. mulleri Gupta and Sharma, 1981 from B. bagarius; B. tripathii Gupta and Sharma, 1981 from Channa striatus; B. gorakhnathai Kumar and Agarwal, 1982 from B. bagarius; B. sohani Agarwal and Singh, 1982 from M. vittatus; B. hemlatae Gupta, 1984 from Rita rita; B. ramalingami Swarup and Jain, 1984 from M. vittatus and B. bagarius; B. kulkarnii Swarup and Jain, 1984 from B. bagarius; B. chauhani Agarwal and Sharma, 1986 from B. bagarius; and B. pedunculata Pandey, Agarwal and Tripathi, 2002 from M. vittatus.

Pandey and Singh (1989) studied the validity of Indian species of Bifurcohaptor and regarded only B. indicus as a valid species, with all others being its synonyms. However, Dubey et al. (1990) regarded B. giganticus, B. son, B. tripathii and B. hemlatae to be valid species, whereas Lim et al. (2001) retained only B. indicus, B. giganticus and B. son as valid species and considered the rest as species inquirendae. Pandey et al. (2002) concluded that catfishes of the Indian sub-continent harbor only two species viz. B. indicus and B. giganticus.

The present description of B. indicus tallies with the original description of the species, with minor modifications in form and measurements of the body structures. B. indicus has been earlier reported from Mystus tengara, M. keletius and M. nemurus (= Hemibagrus nemurus) besides its type host. Dawki and Byrnihat, (Meghalaya), as reported herein, are new locality records for this species.

Polyopisthocotylea

  • Order: Mazocraeidea Bychowsky, 1957

  • Family: Diplozoidae Tripathi, 1957

  • Genus: Diplozoon Nordmann, 1832

  • Diplozoon cauveri Tripathi, 1959 (Figs. 3, 4).

    Fig. 3
    figure 3

    Diplozoon cauveri: a A pair of whole worm in union; b anterior part of the forebody magnified; c single egg magnified; and d single clamp magnified

    Full size image
    Fig. 4
    figure 4

    SEM of Diplozoon cauveri a A pair of whole worm in union (scale bar 200 μm); b view of sub terminal oral sucker showing rough texture with lack of papillae (scale bar 10 μm); c paired opisthaptor in the posterior end showing clamps (scale bar 10 μm); and d magnified single row of clamps (scale bar 10 μm)

    Full size image

Flukes always occurring in permanent pairing, two flukes joined in posterior half of body, in shape of ‘X’; body pale white in colour, forebody longer than hindbody. Prohaptor comprising two cup-shaped suckers. Opisthaptor with four pairs of lateral clamps, rectangular in shape and concave ventrally. Mouth situated on ventral side of anterior extremity; pharynx just behind prohaptoral region. Gut single, intestine not bifurcate but with numerous lateral diverticula. Reproductive organs located in anterior part of hindbody. Testis single, spherical, slightly lobed. Ovary pretesticular. Vitelline follicles extensive, scattered in whole forebody. In utero eggs one, occasionally two in number, oval, without polar filaments. SEM observation showed the presence of rough body surface with absence of spines or papillae. Measurements of the fluke are provided in Table 2.

Table 2 Observations on Diplozoon cauveri Tripathi, 1959
Full size table

  • Host—Labeo pangusia, L. boga

  • Location—Gill filaments

  • Locality—Dawki, Shella, Sonapur (Meghalaya).

Remarks

The genus Diplozoon, with type species D. paradoxum Nordmann, 1832, was first described from the gills of Abramis bramis brama. The species of Diplozoon reported from India so far are: D. indicum Dayal, 1941 from Barbus sarana; D. kashmirensis Kaw, 1950 from Schizothorax niger and S. esocinus; D. soni Tripathi, 1957 from Oxygaster bacaila; D. cauveri Tripathi, 1959 from Cirrhina cirrhosa; D. microclampi Kulkarni, 1971 from Barbus sarana; D. thapari Gupta and Krishna, 1979 from Tor tor and D. dasashwamedhai Agarwal and Kumar, 1989 from Barilius bola.

Fotedar and Parveen (1987) also recorded D. nipponicum Goto, 1891 from Cyprinus carpio specularis from Kashmir. However, Pandey et al. (2002) regarded D. nipponicum Goto, 1891 as a synonym of D. kashmirensis. Further, Pandey and Agarwal (2008) considered D. indicum and D. nipponicum as the only valid species.

The presence of eggs with a long coiled filament is a diagonistic characteristic of the genus Diplozoon. However, D. cauveri was described as having eggs without polar filament (Tripathi, 1959). The present observations of the diplozoid fluke under study tally with the original description of D. cauveri in having non filamented eggs. In view of this character, i.e., eggs without polar filaments, D. cauveri should be recognized as a valid species of the genus. As reported herein, Labeo pangusia and L. boga are new host records and Meghalaya, a new locality record for D. cauveri.