UPV Theses and Dissertations
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Item Molluscicidal activity of tabaco dust against the brackishwater pond snail Telescopium telescopium (Gastropoda: Potamididae)Azucena, Paulene C. (Division of Biological Sciences, College of Arts and Sciences, University of the Philippines Visayas, 2003-04)Telescopium telescopium, a molluscan potamidid snail thrives in the muddy substrates of brackishwater ponds in the Philippines. It occurs in considerable numbers but uncontrollable increases in its population poses serious threats to pond production. Tobacco dust is considered as a potential biomolluscicide that is able to control pond snail infestation. A short-term bioassay was conducted to know the effectiveness of tobacco dust as a molluscicide against T. telescopium by determining its median lethal concentration (LC50) after a period of 96 hours. Twenty-five telescope snails were subjected to varying concentrations of tobacco dust, from 0 to 1.0 kg/L at 0.2-kg increments. Three replicates were done for every treatment. Counting of dead snails was done after 48 and 96 hours of exposure. Snails exposed to varying concentrations of tobacco dust exhibited several defense mechanisms such as avoiding the toxic solution by crawling out of the area, closing their operculum and retracting their bodies toward their shell. Highest snail mortality was observed at the 1.0-kg/L treatment. After the 96-hr. exposure time, the concentration of tobacco dust that proves to be lethal to 50% of the snails was computed to be 0.5849 kg/L. Indeed, tobacco dust is an effective molluscicide against brackishwater pond snails, particularly T. telescopium.Item Nursery and grow-out culture of mangrove polychaete Marphysa sp.Caballero, Pedrita A. (University of the Philippines Visayas, 2019-12)Experiments on the polychaete Marphysa sp. were conducted to determine the optimum stocking density in indoor nursery as well as the optimum stocking density and culture period in outdoor grow-out ponds that can maximize polychaete biomass production. In the nursery experiment, early metatrocophores at four stocking densities (10,000 m-2; 20,000 m-2; 30,000 m-2; and 40,000 m-2) were tested to determine growth (number of chaetigerous segments) and survival after 7 days in nursery cups. Results showed that the number of segments of early juveniles did not vary significantly (P>0.05) in all treatments. Final number of survivors were higher (P<0.05) at 40,000 m-2 (33,700 ± 1,488 ind.) than 10,000 m-2 (8,300 ± 1,097 ind.), 20,000 m-2 (16,100 ± 1,095 ind.) and 30, 000 m-2 (26,800 ± 1,489 ind.). This suggests that Marphysa sp. juveniles can be produced in high numbers despite high stocking densities using the current nursery protocols. The outdoor grow-out experiment was conducted in a brackishwater pond where early juveniles were stocked at four densities(500 m-2; 1,000 m-2; 1,500 m-2; and 2,000 ind.m-2) attwo culture periods (3 and 4 months) to determine the survival and growth of Marphysa sp. Results revealed that stocking density of 500 ind.m-2 resulted in bigger (P<0.05) polychaetes but total length, survival rate, and biomass were not different (P>0.05) from those in higher stocking densities. Survival rates of the polychaetes did not differ significantly (P>0.05) between 4 months (18.1 ± 12.1%) and 3 months(16.1± 9.2%) of culture. Body weight, total length, and polychaete biomass were all significantly higher (P<0.05) after 4 months of culture compared to just 3 months, suggesting longer culture periods can improve overall yields. The organic matter in sediments decreased from 5% to 4% both in treatments for stocking densities and culture periods, indicating the potential of Marphysa sp as a bioremediation agent.