Zoology
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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.