Browsing by Author "Kumara, K.R.P.S."

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Critical better management practices and critical bio-security measures for prevention of entry and spread of white spot virus and pathogenic Vibrio in grow-out farms of cultured Penaeus monodon in Sri Lanka
(Sri Lanka Journal of Aquatic Sciences, 2018) Kumara, K.R.P.S.; Hettiarachchi, M.
Since the first record of white spot disease (WSD) in 1996, PCR tested, white spot virus (WSV) free post larvae of Penaeus monodon (Fabricius 1798) are stocked in grow-out farms as the major bio-security measure. However, significantly high mortality in young shrimp and total rejection of harvest have been recorded in North Western Province, Sri Lanka due to WSD and/or vibriosis. Present study was planned to identify critical better management practices (CBMPs) and critical bio-security measures (CBSMs) that should be strictly adopted to prevent the entry and spread of WSV and pathogenic Vibrio in grow-out farms of P. monodon. A questionnaire survey, carried out at randomly selected 100 grow-out farms located in the North Western Province, revealed that there was a relationship between the occurrence of WSD and /or vibriosis and levels of practicing better management practices (BMPs) and/or bio-security measures (BSMs). Proper pre-stocking pond preparation, adoption of zero water exchange, monitoring and controlling water quality parameters including pathogenic Vibrio in culture water and use of a suitable bioaugmenter and a probiotic were identified as the CBMPs while proper disinfection of culture water, stocking of WSV and MBV free post larvae and prevention of WSV contamination through other routes over the rearing period were the identified CBSMs. Entry and spread of WSV and pathogenic Vibrio in P. monodon grow-out farms in the North Western Province, Sri Lanka could be prevented by strict adoption of CBMPs and CBSMs identified during the present study.
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.
Inadequacy of adopting critical bio security measures and Best Management Practices in Sri Lankan shrimp hatcheries – is controlling vibrio a critical bio security measure?
(Institute of Biology, Sri Lanka, 2013) Kumara, K.R.P.S.; Hettiarachchi, M.; Epa, U.P.K.
Isolation and identification of Vibrio species that cause vibriosis in shrimp (Penaeus monodon ) larvae and its prevention/control using a locally produced probiotic
(University of Kelaniya, 2013) Kumara, K.R.P.S.; Hettiarachchi, M.
Though Sri Lankan shrimp hatcheries use UV sterilized sea water, significant mortalities occur at different larval stages due to vibriosis, if antibiotics are not used to prevent/control it. The present study investigates the sources of contamination, to isolate and identify species of Vibrio and to find out whether vibriosis could be prevented /controlled by a locally produced probiotic containing Bacillus subtillis. Total Vibrio count in incoming water and in different culture facilities was determined, and species of Vibrio isolated from twenty randomly selected shrimp hatcheries were identified. Rearing tanks of two groups of experimental hatcheries were maintained with a probiotic at a concentration of 1× 106CFUml-1 Bacillus subtillis; larvae in one group (E1) were fed with disinfected Artemia nauplii and those in the other (E 2) were fed with non-disinfected Artemia nauplii. Rearing tanks in hatcheries of positive control group were maintained with antibiotics and tanks in negative control group did not receive any treatment; larvae in both controls were fed with non-disinfected Artemia nauplii.
Northeast monsoon rain and associated changes as risk factors for the occurrence of white spot syndrome in cultured Penaeus monodon in the Northwestern province, Sri Lanka
(2008) Kumara, K.R.P.S.
Northeast monsoon rains and associated changes as risk factors for the occurrence of white spot syndrome in cultured Penaeus monodon in the Northwestern province
(Sri Lanka Association for Fisheries and Aquatic Resources, 2009) Kumara, K.R.P.S.; Hettiarachchi, M.
Production of WSSV, MBV and vibrio free good quality post larvae of shrimp, Penaeus monodon without using broad spectrum antibiotics
(Institute of Biology, Sri Lanka, 2013) Kumara, K.R.P.S.; Hettiarachchi, M.; Jayarathne, L.D.
Severity of white spot virus infection and WSV resistance in brood stocks of Penaeus monodon – identified by DNA markers
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Kumara, K.R.P.S.; Hettiarachchi, M.
Huge economic losses that has been occurring in global and national cultured shrimp industry due to white spot disease (WSD) could be controlled if specific pathogen free (“SPF”) and specific pathogen resistant (“SPR”) post -larvae of shrimp for white spot virus (WSV) are stocked in grow-out ponds. Present study investigated whether WSV resistant brood-stocks of Penaeus monodon are available in the coastal sea of Sri Lanka using 317 bp and 71 bp microsatellite DNA markers for the production of “SPF” and “SPR” shrimp post-larvae. Brood stock samples of black tiger shrimp, Penaeus monodon were collected from eight major brood stock collecting sites of the coastal sea of Sri Lanka. DNA from a small piece of a pleopod from each shrimp was extracted and the severity of WSV infection was examined by PCR using IQ200 TM WSV detection kit; extracted DNA was employed to identify WSD-susceptibility and WSD-resistance using 317 bp and 71 bp microsatellite DNA markers. New forward and reverse primers were designed according to 71 bp microsatellite DNA sequence obtained from the data base of National Centre of Bio Informatics for P. monodon. Reaction with IQ200 TM WSV detection kit generated three DNA bands at 720 bp, 310 bp and 210 bp from the WSV genome based on the severity of infection. Brood shrimp collected from Marawila, Chilaw, and Hendala sea recorded a very severe WSV infection that produced all three DNA bands with 105 viral particles. Moderate severity with DNA bands at 310 bp and 210 bp were observed in samples obtained from Negombo sea having 103 to 105 WSV viral particles. Brood shrimp collected from Beruwala, Pottuvill, Mullattivu and Valahchenai recorded a low severity of WSV infection producing DNA band only at 210 bp with 10 to 200 viral particles. Mean percentage prevalence of WSV resistance recorded for brood shrimp collected from Beruwala sea was significantly higher (87.5% ; P < 0.05) being positive for 317 bp DNA band ; those shrimp had significantly low WSD-susceptibility (12.5% mean prevalence being positive for 71 bp DNA band). Highest mean percentage prevalence of WSV-susceptibility was recorded for brood shrimp collected from Chilaw sea (78.1%) while mean prevalence of WSV resistance of the same samples was the lowest (21%). WSV resistant brood shrimp were found in the Sri Lankan coastal sea that could be used to produce “SPF” and “SPR” post larvae which could be a breakthrough in cultured shrimp industry of Sri Lanka. The prevalence of disease resistance in brood stock samples collected from eight major brood stock collecting sites according to both 71 bp and 317 bp microsatellite markers, when ranked in descending order was Beruwala, Pottuvill, Valahchenai, Mullattivu, Marawila, Negombo, Handala and Chilaw. Accession number KX 156833 was received for the genomic sequence of microsatellite DNA marker designed for screening WSV resistance of P. monodon population living in Sri Lankan coastal sea.