WIJAYANANDA, H.I.2021-03-302021-03-302014UWU/AQT/10/0042http://www.erepo.lib.uwu.ac.lk/bitstream/handle/123456789/6321/UWULD%20AQT%2010%200042-09052019093012.pdf?sequence=1&isAllowed=yGlobal bivalve production from aquaculture has consistently increased over the years. Since Sri Lanka has vast natural resources and suitable environmental conditions for aquaculture, it has a great potential for develop and contribute to national fish and shellfish production. Although the bivalve industry is highly developed industry in East Asian region, finfish and shellfish, especially mollusk and sea cucumbers cultures are at very initial stage in Sri Lanka. Sustainable utilization of unexploited high demand finfish and shellfish species are a good alternative to develop the industry. The study was carried out to investigate the possibility to enhance Crassostrea madrasensis culture at Kandakuliya and Gagewadiya in Puttlam district, where the areas are blessed with natural oyster resource which are not used large scale at present. Relationship between variation of water quality parameters and growth performance of Crassostrea madrasensis and prevalence of toxic algae species which cause survival rates were compared in selected culture sites during 10 months (October 2013 to April 2014) period. Temperature, pH, salinity, transparency, depth, nutrients (nitrite, nitrate, phosphate) and unionized ammonia were studied in each site using, glass mercury thermometer, Hach portable pH meter, refractrometer, secchi disk and DR-4000U spectrophotometer according to standard procedures separately. Statistically there were no significant difference (P value > 0.05) in temperature, pH, transparency, depth, nutrients (nitrite, nitrate, and phosphate) and unionized ammonia in two sites except salinity. There were no significant difference (P value > 0.05) in growth (length and width increasing) of C. madrasensis in both sites. Although there were no statistically significant (P value > 0.05) difference between growths in two sites, oysters in Gagewadiya site have shown slightly higher growth rate when compared with Kandakuliya. Further there were significant relationship (P value < 0.05) between length of C. madrasensis and nitrate, temperature, transparency and depth. There were no significant relationship (P value > 0.05) between length and nitrate, phosphate, salinity, unionized ammonia and pH. There were significant relationship (P value < 0.05)between width of C. madrsensis and nitrate, temperature, transparency and there were no significant relationship (P value > 0.05) between width and nitrite, phosphate, salinity, unionized ammonia and pH. Both sites were free from toxic algae and water quality parameters were varied between acceptable range for C. madrasensis survivalenAquatic Resources Technology Degree Programme ( AQT)Thesis