Zoology
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Item Seasonal water-level fluctuations and changes in macro-benthic community structure in tropical reservoirs: A Sri Lankan case study(Lakes & Reserv, 2021) Weerakoon, S.N.; Chandrasekara, W.U.; Amarasinghe, U.S.Seasonal water-level fluctuations (WLFs) in reservoirs influence ecological processes, in turn affecting their benthic macroinvertebrate communities. The present study was carried out in 10 irrigation reservoirs of Sri Lanka to investigate the effects of seasonal WLFs on the benthic macroinvertebrate fauna. The study period was divided into two distinct phases: the drained period and the inundated period. Benthic macroinvertebrates were sampled during both periods and enumerated. Air temperature and soil quality parameters were also measured simultaneously, and hydrological data related to the Kala Oya River basin were obtained from irrigation authorities. Data analysis using non-metric multi-dimensional scaling revealed two distinct reservoir groups, namely, Hydrological Stress Group 1 (HSG1) and Hydrological Stress Group 2 (HSG2). A low hydrological residence time and low relative reservoir level fluctuations (RRLF) characterized HSG1, with the opposite describing HSG2. Temporal variations of macrobenthos indicated a high taxa richness and diversity in HSG1 reservoirs during the drained period, with scrapers and collector-gatherers being the dominant functional feeding groups. Reservoirs in the lower river basin (HSG1) exhibited a high taxa richness and diversity. During the inundated periods, insect taxa colonized, particularly, chironomids and ephemeropterans. Molluscan taxa were prominent during the drained periods. These observations highlight the influence of seasonal fluctuations of reservoir water levels on benthic macroinvertebrates. Benthic macroinvertebrate communities in reservoirs were significantly influenced by the RRLF, manifesting the importance of hydrological regimes in reservoirs to develop macroinvertebrate metrics for water-quality monitoring.Item Habitat related variations and comparison of fatty acid composition of muscle and stomach contents of secondarily colonized Malabar Sprat (Ehirava fluviatilis) in Sri Lanka(NeBIO, An International Journal of Environment and Biodiversity, Vol.10(3), pp.152-163, 2019) de Zoysa, H.K.S.; Amarasinghe, U.S.; Edirisinghe, E.M.R.K.B.; Sundarabarathy, T.V.Ehirava fluviatilis is a marine origin clupeid found in Southern India and Sri Lanka, also found in two freshwater lakes, namely Parakarama Samudraya and Rajanaganaya reservoir, and that places are identified as secondarily colonizedhabitats. The objectives of this study were carried toinvestigate the fatty acid (FA) profile in the flesh of E.fluviatilis, to investigate the FA profile in the food of E. fluviatilis, and identify the impactof the FA profiles for colonisation. The Bligh and Dyer extracting method was used to lipids extraction of flesh and stomach contents of E. fluviatilis and Gas Chromatography (GC) was used to identify the different types of FAs. Data were statistically analyzed to examine the differences in the quantities of different FAs using ANOVA and principal component analysis (PCA). The predominant FAs were recorded in two different habitats ofE. fluviatilis in both flesh) and stomach contents. The only recorded difference between FAs profile was the presence of C 18:2 (n-4) in the Rajanganaya reservoir. The difference in the FA profile may lead to colonization of marine origin E. fluviatilis in Rajanganaya reservoir as a freshwater lacustrine habitat due to the ability of modification of FAs. Further, this study also indicates that the presence of specific FAs could be used as biomarkers to identify species.Item Influence of hydrology on water quality and trophic state of irrigation reservoirs in Sri Lanka(Lakes & Reservoirs: Science, Policy and Management for Sustainable Use, 2019) Nadarajah, S.; Wijenayake, W.M.H.K.; Amarasinghe, U.S.Many reservoirs provide multiple benefits to people around the world, in addition to primary uses such as irrigation. Thus, reservoir management should address their multiple uses. The water quality of ten irrigation reservoirs in Sri Lanka was examined in the present study with the objective of better understanding the effects of hydrological regimes on reservoir water quality and trophic state. Basic limnological parameters pertinent to the nutrient loads to, and trophic state of, the reservoirs were collected from June 2013 to February 2016. The sampling period was arbitrarily divided into two periods of approximately similar duration (period 1 = June 2013–September 2014; period 2 = October 2014–February 2016) to investigate whether or not there was a seasonal variation in the water quality parameters. Although temporal and spatial variations were observed, most water quality parameters were within the levels acceptable for drinking water standards. The 10 reservoirs were also ordinated by principal component analysis (PCA) on the basis of the water quality parameters of the two sampling periods in a two‐dimensional score plot. Reservoirs in the first principal component (PC1) axis were represented by negative scores attributable to the dissolved oxygen concentration and pH and, to a lesser extent, by electrical conductivity and chlorophyll‐a concentration. Positive scores in PC1 were represented by reservoirs with a score loading attributable to alkalinity, nitrate concentration, Secchi depth, temperature and seston weight and, to a lesser extent, from the total phosphorus concentration. There was a significant negative correlation of PC1 scores with relative reservoir water‐level fluctuation (RRLF; the ratio of mean reservoir waterlevel amplitude to mean reservoir depth). Furthermore, Carlson's trophic index also were influenced by RRLF, although not by hydraulic retention time (HRT), indicating allochthonous nutrient inputs into the irrigation reservoirs were mainly governed by RRLF, but not by HRT. Thus, the results of the present study provide useful insights into achieving desirable reservoir water quality through the manipulation of the hydrological regime.Item Comparison of trophic structure of fish assemblages in two tropical steams in Sri Lanka: a seasonal dry zone stream and a perennial wet zone stream(International Review of Hydrobiology, 2019) Weliange, W.S.; Amarasinghe, U.S.; Vijverberg, J.; Leichtfried, M.; Füreder, L.Most tropical rivers especially in the Asian region, are severely impacted by various human perturbations, and the diverse habitats in streams support rich invertebrate and vertebrate communities. It is hypothesized that the fish assemblages and their dietary structure in two tropical streams differ because they flow through different terrains and are exposed to different climatic conditions. In the wet zone stream, which is geomorphological more complex, fish faunal diversity showed significant longitudinal variations, and sustains endemic fish species. In the diets of fish, taxonomic composition was different along the longitudinal gradients, but dietary taxa richness in the two streams was virtually similar having 32 dietary taxa in wet zone stream and 36 taxa in dry zone stream. In the wet zone stream, we observed a lower proportion of specialist feeding species than those in the dry zone stream. Trophic indices of individual species in fish assemblages ranging from herbivory to carnivory also indicate structuring of fish communities along the longitudinal gradients of the two streams based on dietary structure. The main differences between the fish assemblages in the wet zone compared to the dry zone were the higher number of endemic species and the lower percentage of specialist feeders with higher trophic indices. The outcome of this study hopefully contributes to plan future biodiversity conservation management schemes under various river basin development strategies.Item 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.Item Comprehensive evaluation of demographic,socio-economic and other associated risk factors affecting the occurrence of dengue incidence among Colombo and Kandy Districts of Sri Lanka: a cross-sectional study(Parasites & Vectors (2018) 11:478, 2018) Udayanga, L.; Gunathilaka, N.; Iqbal, M.C.M.; Lakmal, K.; Amarasinghe, U.S.; Abeyewickreme, W.Background: Comprehensive understanding of risk factors related to socio-economic and demographic status and knowledge, attitudes and practices (KAP) of local communities play a key role in the design and implementation of community-based vector management programmes, along with the identification of gaps in existing control activities. Methods: A total of 10 Medical Officers of Health (MOH) areas recording high dengue incidence over the last five years were selected from Colombo (n = 5) and Kandy (n = 5) Districts, Sri Lanka. From each MOH area, 200 houses reporting past dengue incidence were selected randomly as test group (n = 1000 for each district) based on the dengue case records available at relevant MOH offices. Information on socio-economic and demographic status and knowledge, attitudes and practices were gathered using an interviewer administered questionnaire. The control group contained 200 households from each MOH area that had not reported any dengue case and the same questionnaire was used for the assessment (n = 1000 for each district). Statistical comparisons between the test and control groups were carried out using the Chi-square test of independence, cluster analysis, analysis of similarities (ANOSIM) and multidimensional scaling (MDS) analysis. Results: Significant differences among the test and control groups in terms of basic demographic and socio-economic factors, living standards, knowledge, attitude and practices, were recognized (P < 0.05 at 95% level of confidence). The test group indicated similar risk factors, while the control group also shared more or less similar characteristics as depicted by the findings of cluster analysis and ANOSIM. Findings of the present study highlight the importance of further improvement in community education, motivation and communication gaps, proper coordination and integration of control programmes with relevant entities. Key infrastructural risk factors such as urbanization and waste collection, should be further improved, while vector controlling entities should focus more on the actual conditions represented by the public on knowledge, attitudes and personal protective practices. Conclusions: The design of flexible and community friendly intervention programmes to ensure the efficacy and sustainability of controlling dengue vectors through community based integrated vector management strategies, is recommended.Item On the retirement of an eminent scientist in fisheries and aquatic science in Sri Lanka: a personal approach(Sri Lanka J. Aquat. Sci. 23(1) (2018): 1-2, 2018) Amarasinghe, U.S.The current issue of Sri Lanka Journal of Aquatic Sciences is dedicated to Professor M.J.S. Wijeyaratne (Department of Zoology & Environmental Management, University of Kelaniya, Sri Lanka) for his 40 years of uninterrupted contribution to research on fisheries and aquatic sciences in Sri Lanka. After his secondary school education at Royal College, Colombo, he entered the University of Sri Lanka, Vidyalankara Campus and was graduated with BSc Special degree in Zoology in 1975 with a Second Class Upper Division Honours. After joining the Vidyalankara Campus of the University of Sri Lanka (presently University of Kelaniya) as a probationary lecturer in 1976, he won the Fulbright scholarship and obtained MSc degree in the field of Natural Resources from University of Michigan, USA in 1978 and subsequently PhD from University of Kelaniya in 1984. During his career, Professor Wijeyaratne has so far authored 100 research papers in indexed journals and scholarly volumes, 14 textbooks and edited volumes, 97 research communications and also contributed as a consultant for 81 development projects both in Sri Lanka and overseas. University of Kelaniya has recently celebrated 50th anniversary of the Faculty of Science. After establishment of the Faculty of Science in this university in 1967, the research culture in the Sri Lankan university system has moved towards a new paradigm, especially in the field of fisheries and aquatic sciences. Professor H.H. Costa, the founder Professor of Zoology in the University of Kelaniya (then Vidyalankara University) was instrumental to make the Department of Zoology in University of Kelaniya the Centre of Excellence in research on fisheries and aquatic sciences in Sri Lanka. Professor Wijeyaratne was the first BSc HonoursItem Influence of Fishing Pressure and Water Level Fluctuations on the Reproductive Biology Traits of Oreochromis niloticus (Linnaeus 1758) in Irrigation Reservoirs of Sri Lanka(Asian Fisheries Science 31 (2018):127–145, 2018) Bandara., K.V.S.N.; Amarasinghe, U.S.The reproductive biological characteristics of Oreochromis niloticus (Linnaeus 1758) were investigated in relation to fishing pressure and water level fluctuation in 10 irrigation reservoirs of Sri Lanka. It was found that matured larger sized male fish made larger and deeper nests. The negative relationship between gonado-somatic index (GSI) and size of maturity (Lm) of female indicates that more energy is utilised for gonadal growth of early matured fish. There were negative relationships of fishing intensity (FI) with egg diameter, Lm, GSI, and condition factor of O. niloticus, showing that heavy fishing pressure in the reservoir fisheries favoured r-selected life strategies. Based on daily water level data of reservoirs, an index to express water availability for a sufficient period, making it possible for the fish to construct nests, termed as water level fluctuation index (WLFI) was calculated. Nest density during peak spawning period was positively related to WLFI. Hence, it was concluded that two anthropogenic factors, FI and reservoir water level fluctuations, influenced reproductive biology attributes of reservoir populations of O. niloticus, which highlighted the necessity for coordination between fisheries and irrigation authorities for augmenting fish yields.Item 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.Item Inland aquatic resources(Natural Resources of Sri Lanka, Chapter 15, 2015) Jayasinghe, J.M.P.K.; Amarasinghe, U.S.Sri Lanka is rich in inland aquatic resources which includes 103 rivers with a cumulative basin area of 59,245 km2, accounting for 90% of the country’s land area. The total extent under inland reservoirs is about 200,000 ha. Most of the reservoirs in the country that include minor irrigation reservoirs and seasonal reservoirs are less than 100 ha in surface area, but are biologically very productive. The inland fishery production from reservoirs of Sri Lanka is essentially a secondary utilization, producing a cheap source of animal protein to the rural communities, which contributes to their nutritional requirements and food security. The inland aquatic resources of Sri Lanka are rich in biodiversity. Introduced fish species, notably the African cichlids, as well as the Chinese and Indian major carps, contribute significantly to inland fishery production which at present is around 75,750 tonnes. There are about 169 species of water birds in Sri Lanka, some of which are resident while others are migrants. These birds assemble in large numbers in wetlands during the migration season, and therefore these locations can be developed into centres of ecotourism. The Country's extensive freshwater and brackish water resources, and the adjoining lowland areas of rivers and reservoirs are potentially a rich resource for food production and income generation for rural populations. There is a vast potential for entrepreneurial investment in inland aquatic resources, such as for value addition of hitherto unexploited or underexploited fishery resources, development of freshwater prawn aquaculture, establishment of ‘fish spa’ using stone sucker Garra ceylonensis, enhancement of ornamental fishing industry, and development of ecotourism and game fishing.