GYRODACTYLUS PRESIDENCYUS SP . NOV . ( TREMATODA : MONOGENEA ) FROM A FRESH WATER TELEOST , CHANNA PUNCTATUS ( BLOCH ) IN WEST BENGAL , INDIA

Members of the Genus Gyrodactylus include viviparous Monogenean ectoparasites characterised by relatively small size, two anterior cephalic lobes, a haptor, a pair of anchors with eight pairs of marginal hooks and a pair of intestinal ceaca ending blindly. They occur on the gills of fresh water and marine fishes. Later, Mizelle and Kritsky (1967) found the species from the skin of the fishes and even on the skin of the frogs (Mizelle et aI., 1969).


INTRODUCTION
Members of the Genus Gyrodactylus include viviparous Monogenean ectoparasites characterised by relatively small size, two anterior cephalic lobes, a haptor, a pair of anchors with eight pairs of marginal hooks and a pair of intestinal ceaca ending blindly.They occur on the gills of fresh water and marine fishes.Later, Mizelle and Kritsky (1967) found the species from the skin of the fishes and even on the skin of the frogs (Mizelle et aI., 1969).
Different species of Gyrodactylus are very narrowly specific as judged by their occurrence in host fishes.Specificity develops over a period of long term mutual adaptation between parasite and host (Bychowsky, 1957).Viviparous Gyrodactylids give birth to individuals containing well developed embryos, have high reproductive rates and these promote effective transmission under crowded conditions.Invasion is caused by adult parasites which transfer directly between adjacent hosts and its intensity increases rapidly and thus kills host directly (Lester and Adams, 1974).Gussev (1978) opined that Indian Monogeneans are found on single species of host (monohostal).
But instances exist when the species of worms occur in more than one host species.Bychowsky (1957) is of the opinion that if this occurs, then the host species belongs to the same genera.Yin and Sproston (1948) disregarded the total consideration and arranged five previously well known species into sub specific ranks on the basis of direction of anchor roots, viz., anterior (G.elegans gr.), inward (G.medius gr.) and outward (G.rasus gr.) and one more subspecies to G. elegans from Gold fish in China.Tripathi (1957), following Sproston (1946) further compounded the confusion describing several well known species to sub specific ranks.He described G. elegans indicus for the first time from India but the description of this new sub species was most inadequate.
A new species of Gyrodactylus viz.G. presidencyus has been proposed and described in this present communication for the first time from West Bengal, India.The type slides will be deposited in the National Collection of the Zoological Survey of India, Kolkata.

MATERIALAND METIIODS
The common snake-headed fish Channa punctatus (Bloch) were collected from a pond of South Bengal (Port Canning, South 24 Parganas, West Bengal) and were brought alive to the laboratory.They were kept in the aquarium with aerated water.Meanwhile, some fishes were observed to be a little discoloured and also found to move listlessly.They were taken out of the water and observed under binocular microscope.The Gyrodactylids were teased out from the surface of the infected regions of the fishes and were fixed directly in AFA for 3-5 minutes in the watchglass.They were stained with semichons' Carnine.Some photomicrographs were taken by Zeiss Axiolab Microscope using MC-80 camera.Measurements were taken with the help of an ocular micrometer.Prevalence: 60% (9 our of 15 host specimen examined).Gussev (1978) held that the peculiarities of chitinoid armament of attachment disk, viz.

Concise keys and supplementary diagnostic features for most species of Gyrodactylids from
Eurasia and North America are available from the works of Gussev(1985) and Beverly-Burton (1984).
Gyrodactylus anguillae has been found to parasitise on eels, Anguilla rostrata and A. anguilla (Malmberg, 1970) and is considered as euryhaline species.Both Gyrodactylus saln10nis and G. colenlanensis are common parasites of salmonid fishes in North America (Cone et al., 1983).
Another species, Gyrodactylus crysoleucas parasitises golden shiner (Notemigonus crysoleucas) and causes significant disease in bait fishes in the southern United States (Lewis and Lewis, 1970).
Gyrodactylus ictaluri has been described from channel catfishes (Ictalurus punctatus) of south eastern United States (Hoffman, 1979) and G. katharineri parasitises Cyprinus carpio throughout Eurasia and caused disease problems in carp ponds.Gyrodactylus turnbulli, a common parasite has been reported from imported Guppies (Poecilia reticulata) of Singapore to England (Harris, 1986).A comparison of diagnostic specific characters of the above parasites with the present described one shows not only differences of measurements but also differences in habitat and host preferences.
Gyrodactylids from Indian water bodies shows inadequate reports (see Dubey et af., 1990 andSingh andAgrawal, 1994).A comparative account of the measurements of different parts of the nine described species of Gyrodactylus from India, including the present one has been presented in the Table I.
I f we consider the chitinoid armament (hard parts) as the key feature of the species demarcation, then the newly described one shows its close proximity with G. recurvensis.Because the anchor measurements (Le.length, superficial root, point) has close reselnblance but the main part (shaft) differs.Again measurements of marginal hook shows similarity but differs highly in deep bar and superficial bar.Although these two species show similarities, close observation reveals G. recllrvensis is smaller in dimension in all aspects of 'hard parts' with the newly described one.
Ifwe consider the other measurements like body length, width, pharynx, haptor etc., there is marked difference between the two species.Actually, G. recllrvensis is almost half or less in length than the presently described species.
Another species G. mizellei shows close resemblance with the presently described one In anchor, superficial bar and marginal hook measurements.But the deep bar differs greatly.'Hard parts' of G. lnizellei are larger in dimension when all the measurements are compared.Comparison shows G. nlizellei is almost three times larger in length than the presently described species.
The hooklet length and shaft (handle) shows resemblance with G. eutheraponsis, but the other parts differs significantly.Even G. eutheraponsis can be well demarked in the species level as it described from a cOlnplete)y different habitat (its host E. therops is a marine fish).
As regard to the anchor measurements of G. hyderabadensis with the described one, the main part, base and point shows .resemblance,but the measurement of marginal hook is quite different and even the other measurements viz. the Jenght of the body, width, pharynx show variations.
number, shape, dimension and functioning of anchors, connecting bars and hooks are of great significance in species and generic diagnosis.Malmberg (1970) had earlier suggested that dimensions and shape of hooks represent the most constant characteristics of species of gyrodactylids of all the armament features.Anchors and connecting bars thus become very important in the species demarcation in gyrodactylids.

Table I .
Comparati ve account of measurements of the different parts of Indian species of Gyrodactylus.(Allmeasurements in microns and range in parentheses)