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The two species of Cestode parasites to be described, viz. Ophryocotyle bengalensis , n. sp., and Bothriocephalus (Anchistrocephalus) Polyptera (Leyd) constitute the first record of any adult Cestode found in any Teleostean fish in Indian waters. Southwell in his examination of marine Teleosts in Ceylon over a period of five years never obtained a single adult Cestode parasite, although encysted larval forms were extremely common. The above two species were obtained from (a) Ophiocephalus striatus (Bengali, Sol ) and (b) Labeo rohita (Bengali, Rohu ). Both species of parasites occurred in each speeies of fish. Those from Labeo rohita were few in number. Those from Ophiocephalus striatus occurred in such large numbers, along with sorne undescribed Trematodes, that the lumen of the intestine of this fish in one particular case appeared entirely choked. Specimens of Ophryocotyle bengalensis , n. sp. were numerous. Only two specimens of Bothriocephalus (Anchistrocephalus) polyptera (Leyd.) were obtained. It has been noted that cystic forms of Cestoda in general are exceedingly common amongst marine Teleosts. On the other hand such cysts are quite rare in freshwater forms. Up to the present I have been unable to discover any except the larva of Ligula simplicissima , which will be referred to later, and this was not encysted, but free in the coelom. Contrary to what occurs in marine fish, adult Cestodes are fairly common in freshwater Teleosts in Bengal, and our examples were obtained from the first fish of the preceding species which we examined. This difference finds an explanation in the widely different conditions existing normally in the sea, and in fresh water. In the sea, adult Cestodes are always found in fish of the shark and ray tribe, which, on the whole, are not subject to the ravages of other predatory fish. In such an host the adult tapeworrns find a safe and secure retreat, from which abode an unending stream of eggs are liberated. [ ... ]
In fresh water, Similarly suitable conditions for the parasite are found in Teleosts, as the larger forms of this group like Labeo rohita , and the voracious Ophiocephalus striatus (which occasionally attains a length of 3 feet or more), are seldom, if ever, preyed upon. There are only two speeies of freshwater rays known in India, viz. Hypolophus sephen (Mull. and Hell.) and Trygon fluviatilis (H.B.), measuring 5 1/2 x 3 1/2 and 4 1/2 x 2 1/2 feet respectively. These are not voracious, and it is improbable that either of them devour large Teleosts.
In the sea, Teleosts are frequently eaten by sharks and rays, and hence we find that Teleosts under these conditions harbour cystic forms only, and that these are capable of maturing and becoming adult in the intestines of their larger and more powerful enemies. In this connection it has already been pointed out (Southwell, 17) that marine Teleosts are not usually intermediate, but collateral hosts to the parasite, and this statement receives strong support from the conditions found to exist in freshwater Teleosts. The larval forms of the parasites to be described have not up to the present been found. It seems probable that they will eventually be discovered encysted either in certain Copepoda on which Labeo rohita feeds, or on the mesenteries of smaller fish such as are devoured by Ophiocephalus striatus .
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Four specimens of an immature species of Distomum were obtained from the intestine of Ophiocephalus striatus , the same specimen of fish in which were found specimens of Opitryocotyle bengalensis , n. sp. and Bothriocephalus (Anchistrocephalus) Polyptera (Leyd.). They measured 9 mm. long and were club-shaped. The breadth at the posterior is 2.5 mm. and at the anterior extremity i mm. The oral sucker is 0.6 mm in diameter. The ventral sucker is situated 4 mm. from the anterior extremity and has a diameter of 0.85 mm. The pharynx is small and no oesophagus is present. The two rami of the intestine are sinuous, terminating blindly at the posterior extremitv. The inwardly directed loop of one ramus of the intestine is situated opposite to the laterally directed loop of the other ramus. Reproductive organs were not developed. It is impossible at present to identify this immature form, but it bears a strong resemblance to the imature form of Isoparorchis trisimilitubis , n. sp., obtained from the muscles of the Mahseer ( Barbus tor ) and already described.
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These passages were originally published under the above title in: Records of the Indian Museum . Vol. 9, part 2, pp. 79-103; 1913. The copyright owner Zoological Survey of India has granted snakeheads.org the right to publish it on the org's site. The copyright of the text is still with the copyright in full amount.
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