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Item 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.Item 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 importantItem Importance of limnological characteristics for the development of culture-based fisheries in non-perennial reservoirs of Sri Lanka(Sri Lanka Association for Fisheries and Aquatic Resources, 2004) Jayasinghe, U.A.D.; Amarasinghe, U.S.; de Silva, S.S.Culture-based fisheries development in non-perennial reservoirs of Sri Lanka is an important strategy for the enhancement of inland fish production. However, little emphasis has been laid on the limnological aspects for planning this extensive aquaculture procedure. The present study was carried out to investigate the possibility of using limnological characteristics of non-perennial reservoirs for future management of their culture-based fisheries. Forty-five reservoirs were randomly selected to study their limnology, of which 32 were stocked with fish fingerlings of Chinese and Indian carps, GIFT variety of Oreochromis niloticus and freshwater prawn at stocking densities ranging from 218 to 3900 fingerlings (or post-larvae) ha-1. Of these, 23 reservoirs were harvested at the end of the culture period (6 – 10 months). Thirteen limnological parameters were measured during the water retention period of each of the 45 reservoirs, between November 2001 and January 2004. Mean values of limnological parameters were used to ordinate reservoirs through principal component analysis. Ordination showed productivity gradient among reservoirs where Secchi disc depth, total phosphorous, chlorophyll-a, inorganic turbidity and organic turbidity were identified as key factors. Total fish yield of culture-based fishery was positively correlated to scores of the first principal component axis. This study reveals that there is a possibility to classify non-perennial reservoirs of Sri Lanka based on limnological parameters such as Secchi disc depth, total phosphorous, chlorophyll-a, inorganic turbidity and organic turbidity in order to develop culture-based fisheries.Item 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.Item 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.Item Limnology and culture-based fisheries in non-perennial reservoirs in Sri Lanka(Lakes & Reservoirs: Research & Management, 2005) Jayasinghe, U.A.D.; Amarasinghe, U.S.; de Silva, S.S.This study was carried out to investigate the possibility of using the limnological characteristics of non-perennial reservoirs in Sri Lanka for the future management of culture-based fisheries. Forty-five reservoirs were randomly selected to study their limnology, out of which 32 were stocked with fish fingerlings of Chinese and Indian carps, tilapia and freshwater prawn at stocking densities ranging from 218?4372 fingerlings ha?1. Of these, 23 reservoirs were harvested at the end of the culture period (6?10 months). Thirteen limnological parameters were measured during the water retention period of each of the 45 reservoirs between November 2001 and January 2004. The mean values of the limnological parameters were used to ordinate the reservoirs through principal component analysis. Ordination showed a productivity gradient among reservoirs where Secchi disc depth, total phosphorus, chlorophyll-a, inorganic turbidity and organic turbidity were identified as key factors. The total fish yield of culture-based fisheries was positively correlated to the scores of the first principal component axis. This study reveals that it is possible to classify non-perennial reservoirs in Sri Lanka based on the above limnological parameters in order to develop culture-based fisheries and that they could be applicable in comparable water bodies elsewhere in the tropics.