Zoology
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Item Fishes and fisheries of Asian inland lacustrine waters(John Wiley & Sons, Ltd, Chichester, UK., 2015) Amarasinghe, U.S.; de Silva, S.S.In tropical Asia, there is a general paucity of natural lakes that are mainly located in the island states of the Philippines and Indonesia. Reservoir construction is extensive in the region primarily for irrigation, flood control and hydroelectricity generation, and fish production is essentially a secondary use of these reservoirs. Although the degree of endemism can in no way be equated to those in the great lakes of rift valley region of East Africa, familial diversity of fishes in Asia, but not species diversity, is considerably higher than in African lakes. Asia has a significant contribution to the world inland capture fisheries production of 11.5 × 106 t that is c. 69%. In most countries in Asia, the bulk of inland fisheries for food fish production occur in lacustrine waters, albeit productive riverine fisheries occur in the Lower Mekong Basin. Nevertheless, fisheries in multipurpose reservoirs are not fully appreciated compared to their other economic uses. Fisheries enhancement in lacustrine waterbodies in Asia through culture-based fisheries (CBF) is considered environmentally friendly due to low external inputs such as provision of supplementary feeds. There is a great potential for food fish production through CBF development in many parts of Asia. Hitherto, deterioration of water quality due to anthropogenic activities is less frequent in Asia than in other regions as local authorities are active in maintaining water quality in reservoirs used for multiple purposes. As reservoir water levels range from highly stable systems to highly fluctuating systems, a combination of flood pulses and mean depth can be used as a fish yield predictor in lakes and reservoirs. Approaches directed towards addressing both human and ecological well-being, in the lake and reservoir fisheries development strategies, are useful to combine the important aspects that are of ecological and societal interest. There is a paucity of studies on climate change impacts on inland fisheries, although some isolated studies are reported on specific aspects. Hence, there is a need to step up research on climate change impacts on inland fisheries for enabling adoption of mitigation and adaptive measuresItem Use of geographical information system and remote sensing techniques for planning culture‐based fisheries in non‐perennial reservoirs of Sri Lanka(Journal of Lakes & Reservoirs: Research & Management, 2014) Wijenayake, W.M.; Gunaratne, A.B.; de Silva, S.S.; Amarasinghe, U.S.The presence of a wide areal extent of small-sized village reservoirs offers a considerable potential for the development of culture-based fisheries (CBFs) in Sri Lanka. To this end, this study uses geographical information systems (GISs) and remote sensing (RS) techniques to determine the morphometric and biological characteristics most useful for classifying non-perennial reservoirs for CBF development and for assessing the influence of catchment land-use patterns on potential CBF yields. The reservoir shorelines at full water supply level were mapped with a Global Positioning System to determine shoreline length and reservoir areal extent. The ratio of shoreline length to reservoir extent, which was reported to be a powerful predictor variable of CBF yields, could be reliably quantified using RS techniques. The areal extent of reservoirs, quantified with RS techniques (RS extent), was used to estimate the ratio of forest cover plus scrubland cover to RS extent and was found to be significantly related to the CBF yield (R2 = 0.400; P < 0.05). The results of this study indicated that morphometric characteristics and catchment land-use patterns, which might be viewed as indices of biological productivity, can be quantified using RS and GIS techniques.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 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 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.