Browsing by Author "Wijenayake, W.M.H.K."

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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.
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.
Diurnal variation in the feeding patterns and food preferences of Dwarf panchax (Aplocheilus parvus)
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Fernando, G.K.A.W.; Jayakody, S.; Wijenayake, W.M.H.K.; Galappaththy, G.N.L.; Yatawara, M.D.M.D.W.M.M.K.; Harishchandra, R.D.J.; Wanninayake, W.M.T.B.; Deniyage, S.L.
The food and feeding studies of fish are useful to explore the possibilities of using them for various purposes such as aquaculture and biological control of problematic organisms. In the current study feeding patterns and diet composition of Aplocheilus parvus (E: Killi fish/Drawft panchax), a common surface feeding predator inhabiting freshwater systems were explored. A. parvus was collected from an abandoned brick pit in Pannala in 2012. Twelve fish were caught every two hours for 24 hours. Plankton net was used to obtain a representative sample of food items present in the system. Gut fullness, total and standard length of fish, total weight and gut weight were determined and using copepod as an arbitrary unit, total numbers of food items of individual fishes were estimated. The time at which active feeding occurred was established from total food particle amount and relative gut weight. Diet of A. parvus mainly consisted of adult or larval stages of insects and copepods. Also, gut had a higher fullness in day time compared to night. The peak gut fullness occurred during 1630 in males whilst females had the peak gut fullness at 1230. Copepods were detected mostly during late morning, whilst insect parts and coleopterans were present in all time periods. Main food items detected in the environment in descending order of abundance were copepods, filamentous algae and insects. This study demonstrated that A. parvus selectively preys on insects compared to other aquatic food sources during day time.
Effect of Hydrological regimes on Fish yield in Reservoirs of Kala Oya River basin, Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Nadarajah, S.; Amarasinghe, U.S.; Wijenayake, W.M.H.K.
Biological productivity of reservoirs is known to be influenced by abiotic factors such as reservoir morphology and hydrological regimes. Seasonal water level fluctuations in reservoirs influence physical, chemical and biological features in reservoirs and thus exert impacts on water quality. It is also a fact that such physio-chemical, biological parameters and the morpho-edaphic factors influence fish yield. As such, the present study was conducted to investigate the influence of reservoir hydrological regimes on fish yield. Water quality parameters were measured in 8 irrigation reservoirs of Kala Oya river basin from June 2013 to December 2014. The hydrological data of reservoirs were gleaned from the Department of Irrigation and Mahaweli Authority. Fish yield data were collected from the fishermen’s log books. Several empirical relationships were derived between abiotic and biotic variables such as total phosphorus, dissolved phosphorus, seston weight, organic weight and chlorophyll-a content against flushing rate (annual outflow/mean reservoir capacity). Also, conductivity, alkalinity, morpho-edaphic indices (MEI) defined as MEIa (alkalinity/mean depth), and MEIc (conductivity/mean depth) had significant positive influences on reservoir fish yield. Conductivity and alkalinity are more significantly related to than fish yield MEIs, possibly due to less variability of mean depth of reservoirs Dissolved phosphorus and seston weight showed strong positive correlation with flushing rate (p<0.05). However, the relationships of total phosphorus and organic weight with flushing rate were not significant at 5% probability level. The flushing rate had a significant second order influence on chlorophyll-a, which perhaps suggests that nutrient enrichment in reservoirs through release of phosphate from the sediments had a greater influence on biological productivity at intermediate levels of flushing rate. There appears to be a negative influence of flushing rate on reservoir fish yield and as such, it can be concluded that through manipulation of hydrological regimes in irrigation reservoirs, fish yields can be optimized. An effective dialogue between irrigation and fisheries authorities is therefore needed for reservoir fisheries management.
The feeding patterns and food preferences of Aplocheilus parvus: a potential biological control agent for malaria?
(Sri Lanka Association for Fisheries and Aquatic Resources, 2012) Fernando, G.K.A.W.; Jayakody, S.; Wijenayake, W.M.H.K.; Yatawara, M.; Harishchandra, R.D.J.; Deniyage, S.L.; Galappaththy, G.N.L.
The ultimate aim of Anti Malaria Campaign is to eliminate indigenous malaria from Sri Lanka. Better environmental and economic benefits could be achieved by the use of indigenous fish species compared to chemical controlling methods as they have minimum or no impact on the existing aquatic fauna. Aplocheilus porvus is a common indigenous species available in both lotic and lentic systems in wet, intermediate and dry zones and is one of the surface feeding predators. The feeding pattern and food preference of A. parvus was determined to test its efficacy as a biological control agent for malaria larvae. A 24 hour sampling for A. porvus wos conducted (n=12 fish every 2 hours) at a brick pit in Pannala MOH region in Northwestern province positive for potential malaria larvae (Anopheles jomesii, 0.1l6/dip) between September 2011 January 2012. Gut fullness, total and standard length of fish, total weight and gut weight and using copepod as an arbitrary unit, total number of food items per 1ml of dissolved gut was calculated with a Sedgewick Rafter Cell. The time at which active feeding occurred was established from total food particle amount and relative gut weight (gut weight/total weighx100). Diet of A. porvus mainly consisted of adult or larval stages of class Insecta (Coleoptera, Hymenoptera and other unidentified insect parts and insect larvae) and class Maxillopoda (Copepoda). Also, gut had a higher fullness in day time (4.3:t0.121) compared to night (2.4:t0.120) (p
Impact of irrigation on reservoir fisheries: Antagonistic or supportive?
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Nadarajah, S.; Amarasinghe, U.S.; Wijenayake, W.M.H.K.
Although reservoirs represent lacustrine ecosystems, they are drastically different from natural lakes for the main reason of prominence of anthropogenic perturbations, which affect ecosystem functioning. Many reservoirs in Sri Lanka are primarily used for irrigation of agricultural lands and are secondarily utilized for inland fisheries production. Effects of hydrological regimes on the biological productivity in reservoirs are therefore expected to have a significant bearing on the fish yield. Aim of this study is to investigate the influence of hydrological regimes on fish yield. In the present study, twelve limnological characteristics of 10 irrigation reservoirs in the Kala Oya river basin of Sri Lanka were investigated from June 2013 to February 2016. Fish yield data in these reservoirs were obtained from the log-book records of fisheries societies. Hydrological data were obtained from the irrigation authorities. Relative water level fluctuation (RWLF), defined as the ratio of amplitude of mean water level fluctuation to mean depth, showed a third order polynomial relationship with chlorophyll-a content (Chl-a) according to, Chl-a = -2.4046 RWLF 3 + 18.732 RWLF 2 - 39.487 RWLF + 44.052 (R² = 0.4351). There was also significant third order polynomial relationship of Chl-a, with fish yield (FY) as: FY = -0.047 Chl-a 3 + 2.689 Chl-a 2 - 45.186 Chl-a + 328.54 (R² = 0.410). As some of the reservoirs in the Kala Oya river basin are terminal reservoirs (e.g., Rajanganaya, Angamuwa, Siyambalangamuwa) from which water is released mainly for irrigation while some are, in addition to irrigation water supply, feeder reservoirs of several downstream reservoirs (e.g., Ibbankatuwa, Kalawewa), effect of hydrological regimes on the biological productivity were possibly represented by polynomial relationships. There was a positive linear relationship between RWLF and FY according to the equation, FY = 27.222 RWLF + 66.729 (R² = 0.586). This indicates that through manipulation of hydrological regimes, reservoir fish yield can be optimized. As such, an effective dialogue should be in place between irrigation authorities responsible for controlling hydrological regimes and authorities responsible for inland fisheries development.
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.
Performance of GIFT strain of Oreochromis niloticus in culture-based fisheries in non-perennial reservoirs, Sri Lanka
(Sri Lanka Journal of Aquatic Sciences, 2007) Wijenayake, W.M.H.K.; Amarasinghe, U.S.; de Silva, S.S.
The superiority of Genetically Improved Farmed Tilapia (GIFT) strain of Oreochromis niloticus has been demonstrated under intensive culture conditions in ponds and cages but its performance under extensive culture conditions and interactions with other cultured species, such as in culture-based fisheries, is unknown. In the present study, performance of GIFT strain in culture-based fisheries in reservoirs of Sri Lanka was evaluated on the basis of specific growth rate, survival, species interaction and biological productivity of habitat. Fourteen non-perennial reservoirs were stocked with carps and GIFT strain and fish yield of all species in the 14 reservoirs studied ranged from 53.4 to 1800.7 kg ha-1, which consisted of 0% to 32% of GIFT strain. Yield of GIFT strain varied from 0% to 188.3 kg ha-1 in the 14 reservoirs. Results of the analysis indicated that biological productivity of the non-perennial reservoirs had greater influence on carp yield than on yield of GIFT strain. Also, there was no significant difference (p > 0.05) between mean fish yields of GIFT strain and non-GIFT strain in culture-based fisheries of non-perennial reservoirs. High variability of specific growth rate of GIFT strain is evident in culture-based fisheries in non-perennial reservoirs. The GIFT strain, which requires supplementary feeding for achieving its maximum growth potential, may be incapable of competing with other species for natural food in the non-perennial reservoirs. As such, GIFT strain is not a suitable candidate for the development of culture-based fisheries in non-perennial reservoirs of Sri Lanka.
Population dynamics of the nymphs of Centroptella ceylonensis Muller-Liebenau and C. Soldani Muller-Liebenau (Ephemeroptera, Baeridae) in the Aswathu oya, Puwakpitiya
(Sri Lanka Association for Fisheries and Aquatic Resources, 2001) Wijenayake, W.M.H.K.; Dias, R.K.S.; Chaminda, K.M.G.R.
Results of a decade of R & D efforts on culture-based fisheries in Sri Lanka
(Network of Aquaculture Centres in Asia-Pacifi c, 2015) Amarasinghe, U.S.; Wijenayake, W.M.H.K.
Fisheries enhancement is defi ned as technical intervention in the life cycles of fi sh. Culture-based fi sheries (CBF) development is one of the major fi sheries enhancement strategies practised in inland reservoirs of Sri Lanka. The extensive availability of inland reservoirs in the country, primarily constructed for irrigation of land crops in ancient times, favours CBF development, which is essentially a development since late 1990s. Water retention period in most small village reservoirs in the country is seasonal and lasts for six to nine months in the year. CBF development in these reservoirs therefore requires fast growing fi sh species such as Chinese and Indian major carps. Hormone induced captive breeding of major carps in government-owned hatcheries and fi ngerlings rearing in mini-nurseries, maintained by rural agricultural farmers, are the sources of seed for stocking these village reservoirs. The CBF in village reservoirs of Sri Lanka is a communal activity involving agricultural farmers without prior experience in fi sheries. As such, awareness programs conducted for these farmers have facilitated establishment of CBF in small village reservoirs. The biological productivity of water bodies and socio-economic conditions of rural communities were found to vary from reservoir to reservoir. As such, successful R&D efforts were made for selection of village reservoirs suitable for CBF development, based on the biological productivity-related parameters such as reservoir morphometry, allochthonous input of nutrients through livestock farming, and socio-economic characteristics of rural communities that favour CBF. For CBF development in village reservoirs, correct timing is necessary for fi ngerling production to suit the monsoonal rainy season when the reservoirs get fi lled. Climate change impacts, which resulted in a shift in peak monsoonal rainy season were therefore identifi ed together with possible resilience capacities of rural communities for sustainability of CBF. Dissemination of research fi ndings through various means such as production of a documentary fi lm, publication of a monograph which was translated to several regional languages, and holding a series of regional workshops were instrumental for CBF development at the regional level. The Asian Development Bank funded Aquatic Resources Development and Quality Improvement Project, which contained a signifi cant component for CBF development in inland reservoirs of Sri Lanka, has also been facilitated by R&D efforts mentioned above. The recent efforts to develop CBF in Sri Lanka include establishment of profi table CBF with effective co-management in selected minor perennial reservoirs, and the use of Macrobrachium rosenbergii post-larvae for CBF in many inland reservoirs.
Strategies for management of culture-based fisheries in seasonal reservoirs of Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2008) Athula, J.A.; Wijenayake, W.M.H.K.; Jayasinghe, U.A.D.
The seasonal reservoirs retain water for 6 to 9 months of the year and completely dry-up yearly or retain very little amount of water for a few months. The extent of seasonal reservoirs estimated to be around 40,000 ha and most of them are located in the dry zone of the country with <200 mm of annual rainfall. These reservoirs are highly productive. Stocking of hatchery-reared fingerlings of Chinese carps, Indian major carps and common carp in these reservoirs resulted in high yields with an average of 449.8 kg ha-1 (range: 53-1,801 kg ha-1). Nearly 60% of the Sri Lankan population mainly depends on fish to obtain the daily requirement of animal protein. According to investigations of the Medical Research Institute, Colombo, minimum fish consumption per day should be at least 60 g, in order to get the daily requirement of protein by fish consumption. As there is about more than 12,000 seasonal tanks scattered as cascade systems throughout the dry zone of the country, which can be utilized for development of culture-based fisheries, they could be used to supply the animal protein requirement of the rural communities. The culture-based fishery activities in seasonal reservoirs depend on both ecological characteristics of the reservoir and the socioeconomic status of village communities. Although the legal empowerment is not yet completed for the culture-based fisheries in seasonal reservoirs, introduction of a set of criteria for the selection of seasonal reservoirs for culture-based fisheries activities on the basis of physical, biological and socioeconomic features and the development of a best practice model for optimization of the yield are important
Use of GIS tools to develop a scale for selection of non-perennial reservoirs for culture-based fisheries activities
(GIS/Spacial Analysis in Fishery and Aquatic Sciences, 2004) de Silva, S.S.; Wijenayake, W.M.H.K.; Gunaratne, A.B.A.K.; Amarasinghe, U.S.