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Item A comparative analysis on the effects of river discharge on trophic interactions in two tropical streams.(International Review of Hydrobiology, 2017) Weliange, W.S.; Amarasinghe, U.S.; Vijverberg, J.; Leichtfried, M.; Füreder, L .Discharge-mediated seasonal patterns of food web interactions were investigated in two streams in Sri Lanka; Eswathu Oya (a perennial wet-zone stream) and Yan Oya (a seasonal dry-zone stream). Based on volumetric proportions of diet composition, relative abundance of fish species and their daily food rations, the mean cumulative consumption of each prey taxon was estimated for each fish population. Food web diagrams were prepared using trophic index of fish, trophic class of prey and feeding interactions between fish and prey. Both streams showed seasonal patterns of discharge due to rainfall, but no significant effect was evident in the trophic index of most fish species. In both streams, cumulative consumption of prey taxa was highest during low discharge regime due to increased abundance of both prey taxa and consumers. In Eswathu Oya, diversity of prey taxa was higher during the low discharge regime, but in Yan Oya, high diversity occurred during the high discharge regime. Herbivorous and/or detritivorous fish species were rare in Eswathu Oya but dominant in Yan Oya. Complex food web structure in Yan Oya due to high fish species richness and high diversity of prey categories made it less sensitive to discharge extremes in contrast to relatively simple food web structure in Eswathu Oya. This study, therefore, highlights the importance of maintaining the quality of riparian environments for conservation of biodiversity.Item Accounting for Diel Feeding Periodicity in Quantifying Food Resource Partitioning in Fish Assemblages in Three Reservoirs of Sri Lanka(Asian Fisheries Society, 2003) Weliange, W.S.; Amarasinghe, U.S.Most investigations on food resource partitioning in fish along the temporal dimension are based on the diet composition of constituent species in fish assemblages, pooled over a longer time lapse, but variation within 24-hour cycle is not considered. In the present study, an attempt was made to account for diel feeding periodicity in fish species in quantifying dietary overlaps among constituent species in fish assemblages in three reservoirs of Sri Lanka. The dietary overlap of fish species estimated as a mean for short time intervals in three reservoirs is significantly lower than that is based on the sum of all time intervals, especially for pairs with moderate and high overlaps. Furthermore, the dietary overlaps estimated for short time intervals, which indicate moderate and high dietary overlaps between pairs, exhibit negligible overlaps of peak feeding period indicating the necessity to account for diel feeding periodicity in quantification of food resource partitioning.Item The Occurrence of Cestode Ligula intestinalis (Linnaeus) from Attentive Carplet Amblypharyngodon melettinus (Valenciennes) in Sri Lanka(Asian Fisheries Society, 2001) Weliange, W.S.; Amarasinghe, U.S.The pleurocercoid stages of Ligula intestinalis (L.) were found in the body cavities of 333 among the 1105 Amblypharyngodon melettinus (Valenciennes) examined from the Victoria Reservoir, Sri Lanka from January 1999 to January 2000. Mean prevalence of this parasite was 23.38%. Mean intensity of infection of L. intestinalis in A. melettinus was 1.006. Mean body condition (CF) of infected A. melettinus was 0.009991 that was significantly different from that of uninfected fish (CF = 0.010445; t = 2.03; p<0.05).The occurrence of this parasite in A. melettinus represents the first record of L. intestinalis in any freshwater fish of Sri Lanka.Item Relationship between Body Shape and Food Habits of Fish from Three Reservoirs of Sri Lanka(Asian Fisheries Society, 2007) Weliange, W.S.; Amarasinghe, U.S.In the present paper, an attempt is made to investigate whether the body shape indices can be used to predict food habits of fish species in three reservoir fish communities of Sri Lanka. The present analysis is based on the studies on food and feeding habits of fish species and their body shape indices in three Sri Lankan reservoirs, namely Minneriya, Udawalawe and Victoria. Body proportions of individual fish species were determined as P1 (= Maximum height of the body/ Maximum width of the body) and P2 (= Total length/ Maximum height of the body), which were found to be negative curvilinearly related. Trophic indices (Ti) of individual fish species were determined on the basis of trophic level of each food item and the fractions of all food items consumed by fish species, which ranged from 1 for exclusively herbivorous species to 3 for carnivorous species. A negative logarithmic relationship between P1 and Ti indicates that laterally compressed fish species with deep bodies feed on lower trophic levels in the food web. On the other hand, dorso-ventrally flattened species with low P1 have higher trophic indices than those with high P1. The positive logarithmic relationship between P2 and Ti also indicates that short, deep-bodied fish species representing low P2 values feed on lower trophic levels whereas slender, long-bodied species with high P2 values feed on higher trophic levels. The body shapes, measured as simple body proportions of the definitions of P1 and P2, can therefore be used to predict feeding habits of fish.Item Diel feeding periodicity, daily ration and relative food consumption in some fish populations in three reservoirs of Sri Lanka(Aquatic Living Resources, 2006) Weliange, W.S.; Amarasinghe, U.S.; Moreau, J.; Villanueva, M.C.Twelve diel surveys were carried out in three reservoirs of Sri Lanka viz. Minneriya, Udawalawe and Victoria, to investigate diel feeding patterns, daily ration and relative food consumption in fish populations. Stomach content weights of different size classes of various fish species in the three reservoirs in 12 diel surveys were analysed using an iterative method, MAXIMS. Predominantly herbivorous or detritivorous fish species such as Amblypharyngodon melettinus and Oreochromis niloticus exhibited one peak in the diel feeding pattern. Two peak feeding periods were evident in predominantly insectivores and/or zooplanktivores (e.g., Puntius chola and Rasbora daniconius) and interestingly in macrophyte feeders (i.e., Etroplus suratensis, Puntius filamentosus and Tilapia rendalli). It might be possible that all species with two feeding peaks in diel feeding patterns rely on vision for feeding. Food consumption per biomass (Q/B ratio) defined as amount of food consumed per unit weight of an age-structured population of fish was estimated on the basis of the average quantities of food consumed over a long period of time by various size classes in order to minimize the bias of estimates.Item Seasonality in Dietary Shifts in Size-Structured Freshwater Fish Assemblages in Three Reservoirs of Sri Lanka(Environmental Biology of Fishes, 2003) Weliange, W.S.; Amarasinghe, U.S.We studied seasonal changes in feeding habits of size-structured fish assemblages in three freshwater reservoirs in Sri Lanka. We obtained fish samples for diet analysis from three reservoirs during the months of rising water level (RIWL) and receding water level (REWL). During RIWL, peripheral areas with terrestrial/semi-terrestrial macrophytes get inundated, which resulted in increased food availability for macrophyte feeding fish. During REWL, detrital food sources increase due to decaying terrestrial plant material, which has inundated. Based on the dietary habits of individual species in the three reservoirs during RIWL and REWL, it is evident that detritivorous and phytoplanktivorous fish species, which belong to low trophic levels do not show significant variation in dietary habits between the two seasons (e.g. Oreochromis mossambicus, Oreochromis niloticus and Amblypharyngodon melettinus). Stenophagous species such as benthic invertebrate predators (Puntius chola and Puntius dorsalis), macrophytophagous species (Etroplus suratensis and Tilapia rendalli) and zooplanktivorous Hemirhamphus limbatus do not exhibit significant variation in dietary habits between seasons. Also their feeding habits do not vary with body size. Euryphagous species such as Puntius filamentosus on the other hand, exhibit variations in dietary habits between seasons as well as with body size. Stenophagous species, which feed on detritus and phytoplankton and euryphagous species, which exhibit temporal dietary plasticity, are therefore abundant in fish assemblages of these reservoirs.