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    Dietary Guild Structure in Fish Assemblages and Trophic Position of Constituent Species in Brush Parks of a Tropical Estuary
    (Asian Fisheries Society, 2019) Gammanpila, M.; Amarasinghe, U.S.; Wijeyaratne, M.J.S.
    Trophic guild structure and dietary niche breadth in tropical fish communities are important to identify functional groups and to understand how trophic positions of constituent species help coexistence. Objective of the present study was to investigate whether the constituent species of fish assemblages in brush parks could be grouped into trophic guilds and how these species contribute to structure the fish community along trophic dimensions. Diets of 46 fish species caught in brush parks were analysed and the food items were categorised into 11 broad groups. Based on the composition of diets, fish were grouped into 8 trophic guilds. Levin’s index of niche breadth indicated that the constituent species in the trophic guilds for which food was abundant, were generalists, whereas the trophic guilds of higher trophic levels were specialists. Within each trophic guild, constituent species showed different trophic indices indicating low inter-specific competition resulting in optimum food resource utilisation.
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    Life history patterns of some selected endemic freshwater fish species inhabiting two major river basins of Sri Lanka
    (Sri Lanka J. Aquat. Sci. 23(1) (2018): 77-84, 2018) Shirantha, R.R.A.R.; Wijeyaratne, M.J.S.; Amarasinghe, U.S.
    Life history information on six endemic fish species namely Belontia signata, Pethiya cumingii, P. nigrofasciata, Puntius titteya, Rasboroides vaterifloris and Garra ceylonensis inhabiting the Kalu Ganga and Kelani Ganga river basins in Sri Lanka was evaluated. The growth constant of the fish species showed a positive relationship with the river order where they inhabited. The length at 50% maturity (Lm) significantly correlated with the asymptotic length and growth constant indicating that fishes with slow growth become sexually mature late in their life cycles. The optimal lengths for sustainable exploitation of the fish species studied were significantly (p<0.01) correlated with asymptotic lengths and lengths at 50% maturity whereas negatively correlated with natural mortality. This analysis indicated that Lm was a foremost function of size of fish apart from maximum length observed (Lmax,) and that Lm and Lmax can be used as deterministic variables for quantifying optimal size of exploitation for sustainability and conservation of fish populations.
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    Morphological correlates with diet of fish assemblages in brush park fisheries of tropical estuaries.
    (Environmental Biology of Fishes., 2017) Gammanpila, M.; Amarasinghe, U.S.; Wijeyaratne, M.J.S.
    Brush park fishery in Negombo estuary, Sri Lanka is a traditional fishing practice which relies on fishes attracted to artificial woody fish aggregation devices. This study investigates whether constituent species in these brush parks exhibit morphological variations in relation to their dietary habits. Fishes caught in brush parks were sampled from April 2014 to April 2016 covering rainy, intermediate and dry seasons. There were 817 specimens of 46 species belonging to 24 families. From each specimen, 17 morphological attributes were determined and diet composition of each species was analyzed in terms of relative biovolume. Trophic index of each species estimated from the proportions of dietary items and their possible trophic level in the community was significantly related to two body proportions (Maximum body height/Maximum body width and Total length/ Maximum body height) which described shape of fish. Principal component analysis of morphometric attributes and dietary habits indicated that the species in the higher trophic levels are characterized by slender, long-body shapes and those occupy lower trophic levels are predominantly laterally compressed with deep body shapes. As such, structure of coexisting species in brush parks of Negombo estuary is predominantly along the trophic dimension and is related to morphological traits of constituent species. The predictive power of ecomorphological correlates with diets of fish species other than mugilids which are attracted to brush parks, can therefore be considered as a useful tool for conducting rapid ecological assessment.
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    Studies on the biology of young grey mullet, Mugil cephalus L.
    (FAO of United Nations, Rome, Italy, 1976) de Silva, S.S.; Wijeyaratne, M.J.S.
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    Trophic condition of Madu Ganga Estuary, a Ramsar Wetland in Sri Lanka
    (2017) Silva, T.M.S.D.G.; Wijeyaratne, M.J.S.
    Madu Ganga Estuary, which extends for 915 ha is a Ramsar wetland in the south- western coastal region of Sri Lanka. This slow flowing water body is rich in biodiversity with 248 vertebrate species which include 20 endemics and 303 plant species. About 10% of the 111 species of birds are winter migrants. Cinnamon and paddy cultivations form the dominant land use type in the surrounding area and at present, a nature based tourism industry is also developing rapidly at the estuary due to its ecological and aesthetic significance. In addition, resident traditional fishermen are involved in commercial fishing activities using traditional gear such as Kraals. The present study aimed to figure out the trophic condition of this important wetland. During the study period from March to November 2014, the mean values for physicochemical parameters were found to be as follows; Depth: 1.89 m; Secchi Depth (SD): 0.91 m; Temperature: 30.8 ˚C; Total Dissolved Solids (TDS): 8.8 g/L; Salinity: 8.29 g/L; pH: 7.2; Dissolved Oxygen (DO): 6.79 mg/L; Biological Oxygen Demand (BOD 5 ): 1.40 mg/L; Nitrate-N: 0.2 mg/L; Total dissolved phosphorous: 0.09 mg/L and Total Phosphorous (TP): 0.17 mg/L. The TP values suggest that the trophic condition of this highly ecologically and economically important wetland is eutrophic. Excess and indiscriminate use of fertilizer in the watershed area and soil erosion appear to be the major reasons for this condition, which may be controlled by educating farmers on repercussions of applying excess amounts of fertilizer and ensuring that only the recommended levels are applied. Remote Sensing methods can also be used in nearby agricultural fields to detect the areas where deficiency symptoms are present and fertilizer can be applied only to those regions. In addition, erosion control methods can also be applied to retain the fertilizer within the agricultural fields without being washed into the estuary with storm water.
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    University research towards sustainable development
    (University of Ruhuna, 2016) Wijeyaratne, M.J.S.
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    Branding, Advertising and Sustainable Development
    (2017) Wijeyaratne, M.J.S.
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    An evaluation of the effect of structural properties of construction materials on the brush parks fishery in the Negombo lagoon, Sri Lanka
    (National Aquatic Resources Research and Development Agency (NARA), Colombo 15, Sri Lanka, 2016) Gammanpila, M.; Amarasinghe, U.S.; Wijeyaratne, M.J.S.
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    Indicating the levels of eutrophication of Diyawanna Lake wetland in Sri Lanka using phytoplankton abundance
    (Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Dilini, R.M.A.; Wijeyaratne, M.J.S.
    Diyawanna Lake is an urban wetland located in Sri Jayewardenepura Kotte. Most areas of this wetland have been rehabilitated recently by digging, restoration of banks and removing aquatic vegetation to increase its water retention capacity to reduce flooding, for recreational purposes and landing sea planes. The non-rehabilitated area in the wetland is rich in biodiversity and provides habitats for several threatened and endemic species. Present study was carried out from March to November 2015 with the objectives of determining the trophic status of the non-rehabilitated and rehabilitated areas and identifying possible indicator phytoplankton species of the trophic conditions. Sampling was carried out in March, May, July, September and November to represent the inter-monsoonal and southwest monsoonal periods in five randomly selected study sites; two in the non-rehabilitated area and three in the rehabilitated area. On each sampling, water and phytoplankton samples were collected from each site in triplicate. Phytoplankton were collected by dragging a 50μ phytoplankton net to a known distance. They were identified to the species level and Sedgwick rafter cell was used to quantitative analysis. Standard methods were used to analyze total nitrate and total phosphorous levels in water samples. Data were analyzed using two way ANOVA. Mean total phosphorous content in the two sites in the non-rehabilitated area (32 and 31 μg/L) were significantly lower (p < 0.05) than those in the rehabilitated area (52, 64 and 57 μg/L). However, these values within each area were not significantly different (p > 0.05). The mean nitrate content in non-rehabilitated area (27 μg/L and 24 μg/L) were also significantly lower (p<0.05) than those in the rehabilitated area (45, 56 and 48 μg/L). These values within each area were also not significantly different (p > 0.05). According to the total phosphorous and nitrate contents, the nonrehabilitated area of can be considered as meso-eutrophic while the rehabilitated area can be considered as eutrophic. A total of 61 species of phytoplankton were identified and none of these species were confined either to meso-eutrophic or eutrophic areas. Hence identification of any particular phytoplankton species as an indicator organisms of meso-eutrophic or eutrophic conditions was not possible. However, abundance of Microcystis aeruginosa, Scenedesmus acuminatus and Melosira islandica were significantly higher and that of Closterium moniliferum was significantly lower in the eutrophic sites than in the meso-eutrophic sites (p < 0.05). According to the present study, abundance of Microcystis aeruginosa above 110 Nos/L, Scenedesmus acuminatus above 30 Nos/L and Melosira islandica above 13 Nos/L indicate eutrophic conditions. Abundance of Closterium moniliferum above 12 Nos/L indicate meso-eutrophic conditions. However, more research using several wetlands is needed to determine the exact ranges of abundance for demarcating the trophic conditions.
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    Trophic ecology and resource partitioning of fish assemblages in brush-parks of Negombo estuary, Sri Lanka
    (Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Gammanpila, M.; Amarasinghe, U.S.; Wijeyaratne, M.J.S.
    three major brush park fishing areas (Munnakkaraya, Katunayake and Dungalpitiya) in Negombo estuary, Sri Lanka were investigated during April 2014 - April 2016 to classify diet composition, evaluate trophic guilds structure, dietary breadths, interspecific dietary overlap and to determine the degree of food resource partitioning of the community. Fraction of food (proportion by volume) consumed by species was used to establish trophic guilds, applying dietary niche breadth, and the inter-specific food niche competition among species was evaluated using Horn’s index. A cluster analysis, based on Euclidean distance resulted in six trophic guilds on the basis of feeding preferences. Although many fishes fed on a diverse range of food items, diets of 15.2% of fish species, which were included in ‘omnivore’ trophic guild, were dominated by algae/macrophytes with less amount of animal matter (omnivores), 23.9% were detritivores, 2.2% were molluscivores, 2.2% were zooplantivores, 17.4% were macro-crustacean predators and 39.1% were piscivores. The trophic levels of the constituent species varied between 1.0 and 3.0 and the both extremes were occupied by about 60% of the species in the fish assemblage. Standardized dietary niche breadth was highly variable. Species in the omnivorous feeding guild (e.g., Gerres oblongus) and those in the detritivorous feeding guild (e.g., Liza subviridis) showed higher dietary niche breadths (>0.82) showing occurrence of wide choices of food categories for them. The species of intermediate trophic class such as Carangoides talamparoides in macro-crustacean feeding guild and those which fed on macro-crustaceans and fish such as Epinephelus sp. and Lutjanus fulviflamma also had broader (>0.88) dietary breadths. The piscivores Sphyraena jello and Terapon puta with highly specialized feeding habits had the narrowest (0.0) dietary breadth. Species which primarily fed on phytoplankton/macrophytes and detritus such as Mugilids and Siganids, and species such as Acanthurus gahhm, Monodactylus argenteus, Scatophagus argus, Etroplus suratensis, Oreochromis mossambicus and Oreochromis niloticus indicated high dietary overlap ranging from 0.50 to 0.97. It was also evident that even majority of the species in the feeding guilds of macrocrustacean predators and piscivores exhibited relatively high dietary overlaps (range 0.1 - 1.0). The present study therefore illustrated that the fish assemblage in brush parks show both food resource partitioning and dietary competition, the former characterizing divergence of resource use to minimize competition for limited food resources and the latter reflecting resource abundance.