ARS - 2005

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Is systemic Vibriosis a predisposing factor for white spot disease in shrimp, Penaeus monodon in grow-out ponds?
(Proceedings of the Annual Research Symposium 2005-Faculty of Graduate Studies, University of Kelaniya, 2005) Hettiarachchi, M.; Hettiarachchi, D.C.
Results of preliminary observations carried out and recorded by some grow out farm managers indicated that the cultured shrimp stocks predisposed to vibriosis are easily susceptible to white spot viral disease. Therefore the present study was carried out in May, 2005 when most of the shrimp grow out ponds at Arachchikattuwa area were affected with white spot disease to see whether there is any relationship between systemic vibriosis and white spot disease. A farm with 5 earthen ponds at Arachchikattuwa area was selected and a commercially available probiotic was used to suppress the Vibrio populations in 3 ponds; other 2 ponds did not receive the probiotic . Weekly random samples of shrimp were observed from each pond and haemolymph was inoculated on TCBS agar and cephalothorax of these shrimp were preserved in Davison Afa for histological preparations. Shrimp in each pond were observed for gross clinical signs of white spot disease. Heamolymph samples obtained from the shrimp of the 2 ponds that did not receive the probiotic treatment gradually increased and reached 480 ± 73 cfu/ml of haemolymph and such shrimp had multifocal melanized and/ or non-melanized haemocytic nodules with septic centers which is the principal diagnostic feature of systemic vibriosis. The stocks of shrimp in these 2 ponds exhibited gross clinical signs of white spot disease within 10-12 days (from the date they had Vibro count of 480±73 cfu/ml of haemolymph) and emergency harvest was carried out. In contrast, haemolymph of shrimp was free of Vibrio in the ponds that received the probiotic treatment and the shrimp did not develop systemic vibriosis and farm manager could complete the normal production cycle. Results of the present study suggest that systemic vibriosis is a predisposing factor for the occurrence of white spot disease in shrimp, P.monodon in grow out ponds.
Pleistophora sp. (a microsporidian) infection in an ornamental fish, swordtail, Xiphophorus helleri ? the first record of the parasite in Sri Lanka
(Proceedings of the Annual Research Symposium 2005-Faculty of Graduate Studies, University of Kelaniya, 2005) Hettiarachchi, M.; Hettiarachchi, D.C.
An aquarium owner in the Western Province of Sri Lanka reported that a stock of swordtail fish that he received from a farm at Ginigathhena area in July, 2005 showed heavy mortality when the fish were kept in two holding facilities in his aquarium. An investigation was carried out to find out the possible cause/s of mortality. Moribund fish were observed for behavioural changes and external clinical signs and then 3 random samples each consisting of 15 fish from each holding facility were obtained. Each fish was euthansiated and necropsy was performed using standard procedure. Tissue samples from affected areas of the body of fish were preserved, histological sections were obtained and observed under the microscope after staining. Affected fish were lethargic and solitary and showed restless swimming at times. The normal reddish orange colour of the fish has been lost at certain places of the skin that covers the dorsal musculature leaving, white patches; these white patches did not have any excess slime formation. Wet mounts of teased muscle from the area of white patches, revealed masses of sporophorous vesicles (pansporoblasts) and typical egg-shaped spores (3.5 µ x 7.5 µ ; with the prominent posterior vacuole which is a diagnostic feature of microsporidia ) were liberated when the sporophorous vesicles were ruptured. Histological sections of the muscle tissue also showed gram positive spores of a Pleistophora sp. in large numbers. There was no other infection / infestation apart from this in moribund fish indicating that the primary cause of mortality was Pleistophora infection in muscles. As there is no proven treatment for microsporidian infections, the owner was asked to destroy the whole stock (few hundreds of remaining fish) and disinfect the holding facilities. This is the first record of Pleistophora infection in Sri Lanka and this is the first record of Pleistophora in swordtail fish.