Browsing by Author "Hettiarachchi, D.C."

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Different isolates of Bacillus subtilis from gastrointestinal tract of wild caught black tiger shrimp, Penaeus monodon to improve a locally produced probiotic/bioaugmenter for controlling pathogenic Vibrio in Sri Lankan shrimp culture systems
(Faculty of Graduate Studies, University of Kelaniya, 2015) Hettiarachchi, D.C.; Kumara, K.R.P.S.; Hettiarachchi, M.
Bacillus species are the major probiotic bacteria used in both hatchery and grow-out systems of tropical shrimp culture industry to control pathogenic Vibrio species. Our previous works have confirmed that the use of a locally produced probiotic/bioaugmenter containing a locally isolated strain of Bacillus subtilis could contribute significantly in producing healthy post larvae of Penaeus monodon and in obtaining a profitable harvest from grow-out ponds compared to systems that did not use the product. Therefore, present study was planned to isolate different isolates of Bacillus subtilis to improve that probiotic or to formulate a new probiotic with improved performances. Samples of apparently healthy black tiger shrimp, P. monodon residing in estuaries in the North Western Province were transported to the laboratory. Gastrointestinal tract samples of the shrimp were first subjected to heat treatment (to kill non-spore forming bacteria) and isolation, purification and characterization of different isolates of Bacillus subtilis were carried out following standard microbiological procedures. Isolates were identified as different strains of Bacillus subtilis by biochemical tests in API 20E and API 50 CHB test kits (bioMerieux, France). Out of the nine different isolates of B. subtilis, only three displayed high growth rate while tolerating wide range of salinity (5gL-1 to 35gL-1) and pH (6 to 10). Antagonistic properties of those three isolates of B. subtilis on five species of pathogenic Vibrio of cultured shrimp in Sri Lanka (isolated and identified in our previous work) were investigated. The diameter of inhibitory zones produced by the new isolates of B. subtilis on the pathogenic Vibrio species ranged from 2 to 4 mm; they could be used to improve the locally produced probiotic/bioaugmentor. The selected three isolates of B. subtilis have been sent for the confirmation of strain type by DNA analysis.
An investigation of caudal fin rot due to Flexibacter collumnaris in guppy, Poecilia reticulata
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2002) Hettiarchchi, M.; Hettiarachchi, D.C.
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.
Isolation of a luminous bacterium that causes heavy mortalities in hatchery reared post larvae of shrimp, Penaeus monodon in Sri Lanka and an attempt to produce vaccines against the bacterium
(Sri Lanka Association for Fisheries and Aquatic Resources, 2004) Hettiarachchi, M.; Pathirage, S.G.; Hettiarachchi, D.C.
Disease outbreaks, detected by a large number of luminescence post larvae in larval rearing tanks followed by heavy mortalities, have been recorded in most of the shrimp hatcheries in Sri Lanka. Broad spectrum antibiotics, probiotics, and occasionally, imported vaccines have been used indiscriminately to control the disease. During the present study, the bacterium causing luminescence in post larvae with heavy mortalities was isolated from seven shrimp hatcheries situated in the North Western Province, characterized, and identified as a strain of Vibrio harveyi using standard microbiological tests and biochemical reactions of bacteria including the tests incorporated to API 20 E rapid diagnostic system. Formalin killed and heat killed vaccines were prepared using the isolated strain of Vibrio harveyi and two groups of eighteen days old healthy post larvae (Pl18 ) were vaccinated with the two vaccines separately by immersion technique. Efficacy of both vaccines was then evaluated by challenging vaccinated post larvae after a week 2 weeks and 3 weeks from vaccination with the same bacteria in live form. Mean percentage survival of post larvae vaccinated with formalin killed vaccine and heat killed vaccine were 81.62% and 80.22 % respectively which were significantly higher ( P < 0.05) than that of the unvaccinated post larvae used as the control (35.21 % and 37.89 %).
Observations on infestations of Piscinoodinium pillularis in freshwater ornamental fish in some commercial aquaria in Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2002) Hettiarchchi, M.; Hettiarachchi, D.C.
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.
Possibility of preventing Acute Hepatopancreatic Necrosis Disease (AHPND), a killer disease in cultured shrimp caused by a unique strain of Vibrio parahaemolyticus if the strain enters into Sri Lankan culture systems
(Institute of Biology, Sri Lanka, 2015) Hettiarachchi, M.; Hettiarachchi, D.C.; Kumara K.R.P.S.
Some aspects of characterization of an unidentified diatom species and its performance as a live food for larval stages of the shrimp, Penaeus monodon
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2002) Hettiarchchi, M.; Hettiarachchi, D.C.
Some growth characteristics of Tetrahymena sp., a parasite of Guppy, Poecilia reticulata and the effect of a mixture of two commonly used Protozoacides on its population density
(Sri Lanka Association for Fisheries and Aquatic Resources, 2003) Hettiarachchi, D.C.; Hettiarachchi, M.