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Item Studies on the fish ponds at Pitipana, Negombo 1. Seasonal and diurnal variation of some hydrobiological factors(The Fisheries Research Station, 1979) de Silva, S.S.; Silva, E.I.L.Item Fish Fauna of a coastal lagoon in Sri Lanka: Distribution and seasonal variation(The Fisheries Research Station, 1979) de Silva, S.S.; Silva, E.I.L.Item Size dependent photosynthetic characteristic of phytoplankton in the Victoria reservoir(Sri Lanka Association for Fisheries and Aquatic Resources, 2003) Amarasinghe, U.S.; Silva, E.I.L.; Weerasinghe, W.M.D.Item Variation of heterotrophic bacterial distribution in Kandy lake(Sri Lanka Association for Fisheries and Aquatic Resources, 2004) Sharaff, F.F.; Silva, E.I.L.; Abeygunawardane, S.I.Kandy Lake, a man-made water body, located in the heart of Kandy adjoining a world famous Buddhist Temple in Sri Lanka was affected by a sudden outbreak of cyanobacteria bloom (Microcystis aeruginosa) in May 1999 with the onset of the southwest monsoonal winds. Many aspects of limnology of this water body have been examined since mid 1990’s. A study based on bacteriology was carried out from July 2001- 2002 July with an objective to understand the distribution pattern of heterotrophic bacteria and their role in eutrophication and pollution. The samples were collected monthly from different depths in the deep and shallow basins. Physicochemical and nutrient analyses of the samples were also carried out simultaneously. Some heterotrophic bacteria were isolated, enumerated and identified up to their generic and species levels using their morphological and biochemical characteristics. The heterotrophic bacteria identified belonged to the genera Bacillus, Pseudomonas and Actinomycetes. Their plate counts were in the range of 106 cfu ml-1. Planktonic bacteria were mainly Gram negative (75%) bacteria. There was no significant (p>0.05) intersite differences with respect to bacterial counts and physicochemical characteristics. However, there was a prominent gradient in the plate counts from top to bottom in the deep basin due to oxygen depletion in the hypolimnion. High coliform counts (1200+/100ml) and faecal coliform counts (550/100ml) were also recorded indicating a high degree of faecal contamination. The results also indicate that the heterotrophic bacteria in Kandy Lake did not show a spatial variation but showed seasonal variation with a marked diversity. Their role in eutrophication is probably through cycling of nutrients such as nitrogen and phosphorus.Item Ecosystem Structure and Dynamics?A Management Basis for Asian Reservoirs and Lakes(Reservoir and Culture-based Fisheries: Biology and Management, 2001) Schiemer, F.; Amarasinghe, U.S.; Frouzova, J.; Sricharoendham, B.; Silva, E.I.L.INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary research program undertaken over the period 1998?2001. Three reservoirs in Sri Lanka (Victoria, Minneriya and Udawalawe) of different morphology, age and geographic location, Ubolratana reservoir, in Thailand, and Lake Taal, in the Philippines, are the object of this study. The scope of the project encompasses a comparison of the limnology, fisheries and socioeconomic aspects of local communities in order to determine whether the trophic characteristics and key ecosystem processes sustain the available fisheries, and to examine the ecological potential for increased fish production by intensive cage culture. The paper first presents integrated results on trophic state, trophic structure and food web relationships of different water bodies. The results demonstrate the importance of ecosystem-orientated analysis in order to optimise management strategies. The broad spectrum of Asian water bodies studied allows testing of a set of hypotheses on: 1) the control of the trophic state of lakes and reservoirs by geographic, climatic and morphometric conditions; 2) the significance of the structure of the fish assemblages (biogeography, exotic species) on ecosystem processes; 3) bottom up versus top down control under Asian reservoir and lake conditions (in comparison to established concepts for water bodies in the temperate zone); and 4) the human impact and resilience of ecosystem processes and trophic conditions towards human impact.Item The occurrence of Cyanobacteria in the reservoirs of the Mahaweli River basin in Sri Lanka(Sri Lanka Association for Fisheries and Aquatic Resources, 1999) Silva, E.I.L.; Wijeyaratne, M.J.S.Item Some aspects of photosynthetic characteristics in a set of perennial irrigation reservoirs located in five river basins in Sri Lanka(Hydrobiologia, 2002) Silva, E.I.L.; Amarasinghe, U.S.; de Silva, S.S.; Nissanka, C.; Schiemer, F.Phytoplankton primary productivity of eleven irrigation reservoirs located in five river basins in Sri Lanka was determined on a single occasion together with light climate and nutrient concentrations. Although area-based gross primary productivity (1.43?11.65 g O2 m?2 d?1) falls within the range already established for tropical water bodies, net daily rate was negative in three water bodies. Light-saturated optimum rates were found in water bodies, with relatively high algal biomass, but photosynthetic efficiency or specific rates were higher in water bodies with low algal biomass, indicating nutrient limitation or physiological adaptation of phytoplankton. Concentrations of micronutrients and algal biomass in the reservoirs are largely altered by high flushing rate resulting from irrigation release. Underwater light climate and nutrient availability control the rate of photosynthesis and subsequent area-based primary production to a great extent. However, morpho-edephic index or euphotic algal biomass in the most productive stratum of the water column is not a good predictor of photosynthetic capacity or daily rate of primary production of these shallow tropical irrigation reservoirs.