Browsing by Author "de Silva, S.S."

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A comparative assessment of the fisheries in lacustrine inland waters in three Asian countries based on catch and effort data
(Fisheries Research, 1991) de Silva, S.S.; Moreau, J.; Amarasinghe, U.S.; Chookajorn, T.; Guerrero, R.D.
The catch and effort data of the artisanal fisheries of the natural lakes and reservoirs in the Philippines, and reservoirs in Sri Lanka and Thailand are evaluated. The yield (kg ha?1 year?1) to effort relationship of the Philippines lakes and Thai reservoirs conformed to a second-order curve, and that of Sri Lankan reservoirs was linear. Similarly, the catch per unit effort (CPUE) to effort per unit area relationships for the Philippines and Thai fisheries were similar and conformed to the Fox model. The relationship of the mean annual yield (kg ha?1) to mean effort in the Sri Lankan reservoirs when considered as a whole, on a yearly basis, conformed to the Schaefer model. On the basis of these relationships the effort which gave the maximum yield per annum was computed for each fishery. The yields were 515, 256 and 93 kg ha?1 for efforts of 20, 6.4 and 10 fishermen for the fisheries of the Philippines, Sri Lanka and Thailand, respectively. An attempt is made to explain the reasons for the apparent differences in these three artisanal fisheries, and the importance of the models in the management of the respective fisheries are discussed. 1 Present address: Deakin University, Warrnambool Faculty of Applied Science and Environmental Technology, P.O. Box 423, Warrnambool 3280, Australia.
A comparative study of the food and feeding habits of Puntius Bimaculatus and P.Titteya (Pisces, Cyprinidae)
(brillonline.com, 1976) de Silva, S.S.; Kortmulder, K.; Wijeyaratne, M.J.S.
A comparison of proximate composition and water stability of three selected Shrimp feeds used in Sri Lanka
(Asian Fisheries Society, Manila Philippines, 2007) Epa, U.P.K.; Wijeyaratne, M.J.S.; de Silva, S.S.
Alien Species in Aquaculture and Biodiversity: A Paradox in Food Production
(AMBIO: A Journal of the Human Environment, 2009) de Silva, S.S.; Nguyen, T.T.T.; Turchini, G.M.; Amarasinghe, U.S.; Abery, N.W.
Aquaculture is seen as an alternative to meeting the widening gap in global rising demand and decreasing supply for aquatic food products. Asia, the epicenter of the global aquaculture industry, accounts for over 90% of the global aquaculture production quantity and about 80% of the value. Asian aquaculture, as with global aquaculture, is dependent to a significant extent on alien species, as is the case for all the major food crops and husbanded terrestrial animals. However, voluntary and or accidental introduction of exotic aquatic species (alien species) is known to negatively impact local biodiversity. In this relatively young food production industry, mitigating the dependence on alien species, and thereby minimizing potential negative impacts on biodiversity, is an imperative for a sustainable future. In this context an attempt is made in this synthesis to understand such phenomena, especially with reference to Asian inland finfish, the mainstay of global aquaculture production. It is pointed out that there is potential for aquaculture, which is becoming an increasingly important food production process, not to follow the past path of terrestrial food crops and husbanded animals in regard to their negative influences on biodiversity.
An evaluation of the role and impacts of alien finfish in Asian inland aquaculture
(Aquaculture Research, 2006) de Silva, S.S.; Nguyen, T.T.T.; Abery, N.W.; Amarasinghe, U.S.
Asia dominates global aquaculture production accounting for over 80% of the total and the mainstay in Asian aquaculture is finfish. Over the years, Asia has experienced a number of inter-continental and intra-continental transfers/introductions/translocation of finfish species, between nations and watersheds, beyond their natural range of distribution, primarily for aquaculture development. In this article all such species are referred to as alien species. An attempt is made to evaluate the importance of the production of alien species in selected Asian nations, using statistics of the Food and Agriculture Organization. Also, negative effects, if any, based on literature surveys, of alien species in relation to displacement of indigenous species, and on biodiversity and/or genetic diversity together with associated pathogen transfers are evaluated. The major alien species, based on their significance to Asian inland aquaculture considered, are the tilapias, catfish, Chinese and Indian major carps and common carp. It is estimated that currently alien species account for nearly 12% of the cultured finfish production (2.6 million tonnes) in Asia, valued at US$ 2.59 billion, and the contribution exceeds 40% when Asian countries excluding China are taken into consideration. Inland finfish aquaculture in some Asian nations, such as Indonesia and the Philippines, is predominated by alien species, and in some others, e.g. Bangladesh and India, the contribution from alien species has been increasing steadily. It is suggested that overall alien finfish species have done little ecological harm to native flora and fauna. However, in the wake of increasing anthropogenic development taking place in watersheds the resulting environments are often made unconducive to indigenous species but not to some alien species, thereby potentially and indirectly making the latter invasive.
An appeal to redefine stunning in Oreochromis mossambicus (Cichlidae)
(Asian Fisheries Forum, 1998) Amarasinghe, U.S.; de Silva, S.S.
Application of a Multiple-criteria decision making approach for selecting non-perennial reservoirs for culture-based fishery development: Case study from Sri Lanka
(Elsevier, 2016) Wijenayake, W.M.H.K.; Amarasinghe, U.S.; de Silva, S.S.
In Sri Lanka, small non-perennial reservoirs (mostly < 50 ha) are numerous in the dry zone receiving less than 185 cm annual precipitation. These are irrigational and are not traditionally used for inland fisheries, due to inadequate natural recruitment, but have the potential for utilization for the development of culture-based fisheries (CBFs), a form of extensive aquaculture. However, the suitability of water bodies for CBF is wide ranging because of the seasonal water retention period and fingerling availability for stocking, variable biological productivity, and community willingness to adopt CBF. In such circumstances multi-criteria decision making (MCDM) approaches are useful for selection of water bodies for CBF. Analytic hierarchy process (AHP), a MCDM approach was employed in this study where, three main criteria (reservoir productivity, catchment characteristics and socio-economic factors) that influence CBF yield were considered. There were two, five and three sub-criteria under each, respectively. As most of the sub-criteria in the analysis are essentially spatial data, it was possible to quantify the influence of each of these on CBF yield using geographical information systems (GIS) and remote sensing (RS) techniques, which were subsequently weighted. Based on the total scores from the weighted linear combinations of the AHP for various sub-categories, the reservoirs were categorized for their suitability for CBF in to four levels as excellent, good, fair and poor. As there was a positive significant relationship between the total AHP score and CBF yield, it was concluded that use of AHP based weighted linear combination would be a feasible approach for selection for CBF development, and that this methodology would be applicable to comparable situations in the tropical region.
An approach to classify seasonal reservoirs of Sri Lanka using Carlson’s Trophic State Index
(Sri Lanka Association for Fisheries and Aquatic Resources, 2003) Jayasinghe, U.A.D.; Amarasinghe, U.S.; de Silva, S.S.
Better-practice approaches for culture-based fisheries development in Asia
(Australian Centre for International Agricultural Research, 2006) de Silva, S.S.; Amarasinghe, U.S.; Nguyen, T.T.T.
Counselling for interpersonal conflict: a model based on Buddhist principles
(2014) de Silva, S.S.
Culture-based fisheries in non-perennial reservoirs in Sri Lanka: production and relative performance of stocked species
(Fisheries Management and Ecology, 2005) Wijenayake, W.M.H.K.; Jayasinghe, U.A.D.; Amarasinghe, U.S.; Athula, J.A.; Pushpalatha, K.B.C.; de Silva, S.S.
In Sri Lanka, there is a great potential for the development of culture-based fisheries because of the availability of around 12 000 non-perennial reservoirs in the dry zone (<187 cm annual rainfall) of the island. These reservoirs fill during the north-east monsoonal period in October to December and almost completely dry up during August to October. As these non-perennial reservoirs are highly productive, hatchery-reared fish fingerlings can be stocked to develop culture-based fisheries during the water retention period of 7?9 months. The present study was conducted in 32 non-perennial reservoirs in five administrative districts in Sri Lanka. These reservoirs were stocked with fingerlings of Indian (catla Catla catla Hamilton and rohu Labeo rohita Hamilton) and Chinese (bighead carp Aristichthys nobilis Richardson) major carps, common carp Cyprinus carpio L., genetically improved farmed tilapia (GIFT) strain of Nile tilapia, Oreochromis niloticus (L.) and post-larvae of giant freshwater prawn, Macrobrachium rosenbergii De Man, at three different species combinations and overall stocking densities (SD) ranging from 218 to 3902 fingerlings ha?1, during the 2002?2003 culture cycle. Of the 32 reservoirs stocked, reliable data on harvest were obtained from 25 reservoirs. Fish yield ranged from 53 to 1801 kg ha?1 and the yields of non-perennial reservoirs in southern region were significantly (P < 0.05) higher than those in the northern region. Naturally-recruited snakehead species contributed the catches in northern reservoirs. Fish yield was curvilinearly related to reservoir area (P < 0.05), and a negative second order relationship was evident between SD and yield (P < 0.05). Chlorophyll-a and fish yield exhibited a positive second order relationship (P < 0.01). Bighead carp yield impacted positively on the total yield (P < 0.05), whereas snakehead yield impact was negative. Bighead carp, common carp and rohu appear suitable for poly-culture in non-perennial reservoirs. GIFT strain O. niloticus had the lowest specific growth rate among stocked species and freshwater prawn had a low return.
Culture-based fisheries in non-perennial reservoirs of Sri Lanka: influence of reservoir morphometry and stocking density on yield
(Fisheries Management and Ecology, 2006) Jayasinghe, U.A.D.; Amarasinghe, U.S.; de Silva, S.S.
Culture-based fish yield in non-perennial reservoirs of Sri Lanka was related to reservoir morphometry and stocking density. The reservoirs were stocked mainly with fingerlings of one Chinese and three Indian major carp species, common carp, Cyprinus carpio L., and the genetically improved farmed tilapia strain of Nile tilapia, Oreochromis niloticus (L.), at four pre-determined species combinations and a range of stocking densities [SD (fingerlings ha?1)]. Twenty-three reservoirs were harvested successfully at the end of the culture period of 2002?2003. Basic limnological and morphometric parameters, including shoreline development (DL) and shoreline area ratio (RLA), were estimated for each of the 23 reservoirs. Bray?Curtis similarity and non-metric multidimensional scaling using mean values of limnological data revealed that reservoirs could be ordinated into two major clusters, one with intact sample distribution due to similar trophic characteristics and the other with scattered sample distribution. Reservoirs in the cluster with similar trophic characteristics showed significant correlation (P < 0.05) between RLA and total fish yield (Y). A multiple regression equation, Y = ?693 + 4810 RLA + 0.484 SD, was generated to estimate fish harvest in relation to SD.
Diel feeding patterns and daily ration of cyprinid species in the wild determined using an iterative method, MAXIMS
(Journal of Fish Biology, 1996) de Silva, S.S.; Amarasinghe, U.S.; Wijegoonawardena, D.N.S.
Diel feeding patterns and daily food rations of five cyprinids Amblypharyngodon melettinus, Barbus chola, B. dorsalis, B. filamentosus and Rasbora daniconius in two Sri Lankan reservoirs were studied based on diel surveys using an iterative method, MAXIMS. A. melettinus and B. chola had single peaks of feeding whereas diel feeding patterns with two peaks occurred in the other three species. Daily food rations varied seasonally and with size of fish. The iterative technique used is reliably applicable for quantifying daily rations, and provides a means of linking trophic levels in natural populations of fish.
Effect of a commercial bacterial production water quality and shrimp production in low water exchange shrimp culture ponds in Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2005) Epa, U.P.K.; de Silva, S.S.; Widanapathirana, G.S.
Empirical Approaches for Evaluating Efficiencies of Different Fishing Methods in Tropical, Shallow Reservoirs : A Sri Lankan Case Study
(Reservoir Fisheries of Asia, 1992) Amarasinghe, U.S.; de Silva, S.S.
Evaluation of community participation for the development of culture-based fisheries in village reservoirs of Sri Lanka
(Aquaculture Economics & Management, 2009) Kularatne, M.G.; Amarasinghe, U.S.; Wattage, P.; de Silva, S.S.
Evaluation of Feed Management Strategies in Shrimp Culture Ponds in Sri Lanka
(University of Kelaniya, 2005) Epa, U.P.K.; Wijeyaratne, M.J.S.; de Silva, S.S.
Shrimp exports have become one of Sri Lanka’s major foreign exchange earners and accounts for nearly 90% of total aquaculture exports. The average feed costs for the Sri Lankan shrimp culture industry is estimated to be around 54% of the total recurrent costs. This study evaluated different feed management strategies in commercial shrimp farms with a view to bringing about improvements. Five shrimp farms with different management practices in the north western province, Sri Lanka were selected for the study. Feed selection, storage methods, feed types, feeding frequency, ration size, feeding tray monitoring, adjustments to feeding rates, and feed conversion ratios (FCR), specific growth rate (SGR) of shrimp were recorded weekly. Blind feeding was employed in all the farms from date of stocking to 30 – 45 days. It varied from 131.5 – 219.8 kg/ 100,000 post larvae and did not increase simultaneously with stocking density. No correlation was found between the amount of feed given with SGR during the blind feeding period (p > 0.05). These results suggest the probability of over feeding during the initial stage of the culture cycle. Adjustments to feeding rates were done according to feed tray (6 – 8 trays / ha) observations, feeding guide supplied by feed manufactures and theoretical survival calculations. Feed tray observation time varied from 1 h to 2.30 h. Feeding frequency was 2 – 6 times a day. Higher variation of these parameters emphasizes the need to standardize them for optimum feed usage. Four feed management information transfer channels were identified in shrimp farms. These were (i) owner - feed marketing officer (ii) labourer – manager - consultant (iii) supervisor - manager (iv) manager only. FCR values in the farms were 2.0, 1.5, 1.4, 1.4 – 1.3 with SGR of 2.5, 2.9, 3.3, 2.6 day-1, respectively. Information channels (i) and (ii) resulted in higher FCR values. It is suggested to pay more attention on information transfer channels in order to avoid over- feeding. Blind feeding, feeding frequencies and information transfer channels were identified as crucial areas that could be improved for the sustainable shrimp culture industry in Sri Lanka. With these improvements, the cost of feeding could also be minimized.
Evaluation of the robustness of predictive yield models based on catchment characteristics using GIS for reservoir fisheries in Sri Lanka
(Fisheries Management and Ecology, 2002) Amarasinghe, U.S.; de Silva, S.S.; Nissanka, C.
Land-use patterns in the catchment areas of Sri Lankan reservoirs, which were quantified using Geographical Information Systems (GIS), were used to develop quantitative models for yield prediction. The validity of these models was evaluated through the application to five reservoirs that were not used in the development of the models, and by comparing with the actual fish yield data of these reservoirs collected by an independent body. The robustness of the predictive models developed was tested by principal component analysis (PCA) on limnological characteristics, land-use patterns of the catchments and fish yields. The predicted fish yields in five Sri Lankan reservoirs, using the empirical models based on the ratios of forest cover and/or shrub cover to reservoir capacity or reservoir area were in close agreement with the observed fish yields. The scores of PCA ordination of productivity-related limnological parameters and those of land-use patterns were linearly related to fish yields. The relationship between the PCA scores of limnological characteristics and land-use types had the appropriate algebraic form, which substantiates the influence of the limnological factors and land-use types on reservoir fish yields. It is suggested that the relatively high predictive power of the models developed on the basis of GIS methodologies can be used for more accurate assessment of reservoir fisheries. The study supports the importance and the need for an integrated management strategy for the whole watershed to enhance fish yields.
Extent of the catchment of reservoirs of Sri Lanka: an important aspect in the management of their capture fisheries
(Asian Fisheries Forum, 1998) Nissanka, C.; Amarasinghe, U.S.; de Silva, S.S.
Feasibility of rearing Labeo rohita (Hamilton) fry in cages with community participation: A case study in Sri Lanka
(National Aquatic Resources Research and Development Agency, 2007) Ariyaratne, M.H.S.; Wijeyaratne, M.J.S.; de Silva, S.S.