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    Effects of biological and technical factors on brain and muscle cholinesterases in Nile tilapia, Oreochromis niloticus: implications for biomonitoring neurotoxic contaminations
    (Springer-Verlag., 2008) Pathiratne, A.; Chandrasekera, L.W.H.U.; De Seram, P.K.C.
    Influence of body length, body weight, gender, sexual maturity, and tissue storage on brain and muscle cholinesterases (ChE) in Nile tilapia was evaluated considering its potential use in biomonitoring neurotoxic contaminations in tropical environments. Results show that ChE activities in both tissues decreased significantly with increased total length (4–24.5 cm) or body weight (1–186 g) of the fish and the relationships were curvilinear. Comparisons of the slopes and elevations of the regression lines of the logarithmic ChE and body size relationships of males with those of females indicated that gender had no significant effect on the body size-specific ChE activities. Response of the ChE of sexually mature males to chlorpyrifos exposure was similar to that of females. Gonadal maturity stage of this fish does not seem to influence ChE activities. Storage of tissues at –80°C for 28 days had no significant effect on ChE activities in the control fish and the fish exposed to carbofuran. However, a partial reactivation of brain ChE activities was observed in the fish exposed to carbosulfan after 28 days of storage. The results emphasize the importance of consideration of body size of the fish and storage time of the tissues in order to formulate accurate conclusions about the neurotoxic chemical exposure when ChE of the fish is used in biomonitoring programs.
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    Traditional Practices for Resource Sharing in an Artisanal Fishery of a Sri Lankan Estuary
    (Asian Fisheries Society, 1997) Amarasinghe, U.S.; Chandrasekera, L.W.H.U.; Kithsiri, H.M.P.
    In the Negombo estuary of Sri Lanka, there is an artisanal fishery for penaeid shrimp locally known as stake-seine fishery. Stake-seine nets, which can be fixed in specific sites close to the sea mouth, are used for catching shrimp that migrate from the estuary to the sea. According to regulations imposed by the fishing communities, use-rightss in the fishery are granted to descendants of certain fishing families in four villages. Among the stake-seine fishers who are organized into four rural societies, an effective mechanism has been evolved for resource sharing in the fishery over a period of several hundred years. For equity sharing of the resource, different fishing dates are assigned to the four rural societies, and fishing sites are allocated to individual fishers in each society using a lottery system. Sustenance of this traditional practice is due to the fact that the returns from the fishery are significant. Community-based management strategies for the fisheries in developing countries can therefore be defined by adopting relevant mechanisms found in these types of artisanal fisheries.
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    Use of biomarkers in Nile tilapia to assess the impacts of pollution in BolgodaLake, an urban water body in Sri Lanka
    (Environmental Monitoring and Assessment, 2009) Pathiratne, A.; Chandrasekera, L.W.H.U.; Pathiratne, K.A.S.
    The present study reports the first analysis of water pollutants in Sri Lankan waters using a suite of biomarkers in Nile tilapia (Oreochromis niloticus) residing in Bolgoda Lake which receives urban, industrial and domestic wastes from multiple sources. The fish were collected from the lake in the dry period (April 2005) and wet periods (September 2005, October 2006) and the levels of biomarkers viz. hepatic ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST), metallothioneins, biliary fluorescent aromatic compounds, brain and muscle cholinesterases (ChE) were compared with those of the laboratory reared control fish and the fish obtained from a less polluted water body, Bathalagoda reservoir (reference site). The results revealed that biomarker levels of the fish collected from the reference site were not significantly different from the controls. Hepatic EROD and GST activities in fish from Bolgoda Lake were induced 4.2?16.6 folds and 1.4?3.3 folds respectively compared with the control fish. Analysis of bile in the lake fish revealed recent uptake of naphthalene, pyrene and benzo(a)pyrene type polycyclic aromatic hydrocarbons (PAHs). The induction of EROD activities in feral fish reflects the exposure of fish to aryl hydrocarbon receptor agonists including PAHs present as pollutants in the Bolgoda Lake. Cholinesterase activity in the fish inhabiting one sampling site of Bolgoda Lake was lower (22?40% inhibition) than the activity measured in the control fish indicating the presence of anticholinesterase pollutants in the area. Hepatic metallothionein levels in the lake fish were higher (1.9?3.2 folds) in comparison to the controls indicating metal exposure. The results support the potential use of these biomarkers in Nile tilapia in assessing pollution in tropical water bodies.
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    Effect of biological and technical factors on brain and muscle cholinesterases in Nile Tilapia(Oreochromisniloticus): Implications for biomonitoring neurotoxic contaminations
    (Archives of Environmental Contamination and Toxicology, 2008) Pathiratne, A.; Chandrasekera, L.W.H.U.; de Seram, P.K.C.
    Influence of body length, body weight, gender, sexual maturity, and tissue storage on brain and muscle cholinesterases (ChE) in Nile tilapia was evaluated considering its potential use in biomonitoring neurotoxic contaminations in tropical environments. Results show that ChE activities in both tissues decreased significantly with increased total length (4?24.5 cm) or body weight (1?186 g) of the fish and the relationships were curvilinear. Comparisons of the slopes and elevations of the regression lines of the logarithmic ChE and body size relationships of males with those of females indicated that gender had no significant effect on the body size-specific ChE activities. Response of the ChE of sexually mature males to chlorpyrifos exposure was similar to that of females. Gonadal maturity stage of this fish does not seem to influence ChE activities. Storage of tissues at ?80?C for 28 days had no significant effect on ChE activities in the control fish and the fish exposed to carbofuran. However, a partial reactivation of brain ChE activities was observed in the fish exposed to carbosulfan after 28 days of storage. The results emphasize the importance of consideration of body size of the fish and storage time of the tissues in order to formulate accurate conclusions about the neurotoxic chemical exposure when ChE of the fish is used in biomonitoring programs.
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    Effects of waterborne cadmium on biomarker enzymes and metalothioneins in Nile tilapia, Oreochromis niloticus
    (Journal of National Science Foundation of Sri Lanka, 2008) Chandrasekera, L.W.H.U.; Pathiratne, A.; Pathiratne, K.A.S.
    Cadmium is widely used in modern industry and ranks among the most toxic metals in the aquatic ecosystems. In the present study, activities of several biomarker enzymes viz. ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and cholinesterase (ChE) were determined in Nile tilapia (Oreochromis niloticus) at different waterborne Cd22+ exposure levels (0, 0.001, 0.005, 0.01, 0.1, and 1 mg/L for 28 days) to evaluate the potential influence of environmental cadmium on these enzymes. In addition, hepatic metallothionein (MT) levels in these fish at different waterborne Cd2+ exposure levels were also studied to evaluate their response to waterborne cadmium exposure. The results revealed that hepatic MT levels in the fish exposed to Cd2+ increased 2-26 fold depending on the exposure level and duration. Hence hepatic MT in Nile tilapia is a sensitive biomarker to indicate cadmium pollution in the natural environments. Continuous exposure of fish to ? 0.01 mg/L of Cd2+ had no significant effect on hepatic EROD, hepatic GST and brain and muscle ChE activities whereas exposure to ? 0.1 mg/L Cd2+ evoked time dependent significant depression of hepatic EROD (41-55%) activity. Brain and muscle ChE activities of the fish exposed to 1 mg/L Cd2+ were depressed to 24-32% and 33-35% respectively. Results revealed that high concentrations of Cd2+ in the natural environments could inhibit the basal activities of the hepatic EROD and brain and muscle ChE in Nile tilapia affecting the normal functioning of these biomarker enzymes and influencing the biomarker response to targeted organic pollutants in the environment.
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    The restoration of mud flats invaded by common cord-grass (Spartina anglica, CE Hubbard) using mechanical disturbance and its effects on the macrobenthic fauna
    (Aquatic Conservation: Marine and Freshwater Ecosystems, 1999) Frid, C.L.J.; Chandrasekera, L.W.H.U.; Davey, P.
    1. The growth of the common cord-grass, Spartina anglica, across many temperate coastlines has resulted in a reduction in the extent of tidal flats. Its colonization has reduced the abundance of macrobenthic fauna and hence has had a direct effect on the feeding of shorebirds. Although the use of chemical methods has proven successful in controlling Spartina swards on tidal flats, factors such as environmental and human health concerns have stimulated a search for alternative control methods. However, any such control method must not impact the macrobenthic fauna. 2. The effectiveness of a physical disruption to control Spartina swards on tidal flats was investigated in the saltmarsh at Lindisfarne NNR, UK. The sediment was disturbed by a light-weight tracked vehicle until the Spartina swards were dislodged and buried within the sediment. The post-disturbance dynamics of the infauna in the disturbed area was investigated 1, 12, 31, 92 and 384 days after the disturbance. 3. In spite of the drastic change brought about in the flora, there was no evidence that the infauna were impacted by the disturbance at any sampling time. Two possible mechanisms to explain the absence of changes in the abundance of the infauna are discussed with special reference to the unconsolidated nature of the sediment and the high mobility of the adult infauna. The abundance of Spartina swards in the disturbed area was lower than that in the undisturbed area. Physical disturbance to Spartina swards by the tracked vehicle seems to be an appropriate method for its control in tidal flats which obviates the need, with associated financial costs and environmental risks, of chemical control.
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    Alaboratoryassessment of the survival and verticalmovement of twoepibenthicgastropodspecies, Hydrobia ulvae (Pennant) and Littorina littorea (Linnaeus), afterburial in sediment
    (Journal of Experimental Marine Biology and Ecology, 1998) Chandrasekera, L.W.H.U.; Frid, C.L.J.
    Physical disturbance may result in the burial of the epibenthic fauna in sediment. The patches thus created undergo a `recovery' which may include the buried fauna migrating through the sediment to regain their original position in the sediment. A series of laboratory experiments were carried out to investigate the effects of prolonged burial on twoepibenthicgastropodspecies, Hydrobia ulvae and Littorina littorea, under various sediment temperature regimes. Their ability to regain the sediment surface under simulated winter (i.e. 7.5�C) and summer (i.e. 20.3�C) temperature conditions was studied in relation to the depth and the duration of burial. The effects of sediment silt and water content was also examined in a separate experiment. The proportion of H. ulvae surviving burial in natural sediment to 5 cm depth decreased with increasing duration of burial and sediment temperature. Burial to 5 cm was fatal to L. littorea within 24 h at all the temperatures examined. In sediment mixtures which had, by dint of large interstitial spaces, a good supply of oxygen or which were very fluid (i.e. `high silt-high water' sediment) a large proportion of H. ulvae and L. littorea regained the surface within 1 day of burial. No individuals of either species regained the surface in sediment mixtures with high silt and low water contents, this included the unaltered natural sediment treatment. In all cases, the depth of burial significantly reduced the surface regaining ability of L. littorea while it had no effect on H. ulvae. The survival and the escape behaviour of buried H. ulvae and L. littorea is discussed in relation to their respiratory metabolism and the oxygen stress in the sediment. The potential contribution of the buried fauna to the recovery of soft-bottom patches is assessed.
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    Effects of human trampling on tidalflat infauna
    (Aquatic Conservation: Marine and Freshwater Ecosystems, 1996) Chandrasekera, L.W.H.U.; Frid, C.L.J.
    1.?Human trampling has been shown to be detrimental to the survival of fauna of terrestrial habitats and on rocky coastal areas. However, its effects on saltmarsh benthic infauna were not known. 2.?The abundance of macro-benthic fauna at five locations on a transect across a footpath on the emergent marsh and on the tidalflat at Lindisfarne NNR were sampled during the summer 1994 and winter 1995. 3.?The abundances of dominant taxa increased in summer in the intensely trampled path on the unvegetated tidalflat leading to a change in the community structure. These changes were not apparent when the trampling intensity was lower in winter. 4.?The abundances of dominant taxa at a less intensively trampled site in the vegetated emergent marsh did not change in either season. 5.?The susceptibility of the saltmarsh infauna to human trampling depends on the intensity of trampling disturbance and on the nature of the habitat. The possible effects of human trampling on the macrofauna in these intertidal habitats are discussed with reference to coastal management.
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    The effects of Relic fauna on initial patch colonisation in a British saltmarsh
    (Netherlands Journal of Aquatic Ecology, 1996) Chandrasekera, L.W.H.U.; Frid, C.L.J.
    When a disturbance impacts an area it rarely leads to a complete defaunation, some individuals survive forming a relic fauna. Relic fauna in azoic patches in an intertidal soft-bottom habitat were simulated by the separate introduction of individuals ofNereis diversicolor, Hydrobia ulvae andLittorina littorea into defaunated cores. These were exposed in the field for 24 hours and the effects of relics on colonisation were assessed separately for colonisation via the sediment surface and colonisation via the surface and laterally through the sediment. After 24 hours all the species in the ambient community were recorded from at least some experimental cores. Densities of the most abundant infaunal taxa,Corophium volutator, Enchytraeus buchholzi, Manayunkia aestuarina, Tubificoides benedeni and nematodes, varied between 1% and 279% of ambient. MDS ordinations showed significant differences in the fauna of experimental cores, a result of the lack of full colonisation by some species and the presence of other species at densities in excess of ambient. Comparisons (ANOSIM and ANOVA) of the fauna of the relic addition cores vs. no-addition cores showed an influence ofN. diversicolor on colonisation. However, this relic effect appeared to be masked by the high degree of variation in colonisation. Densities ofL. littorina andH. ulvae were not maintained in all of the experimental cores and there was no significant difference in the fauna of cores in which the treatments were maintained. It therefore seems that initial colonisation of patches in the emergent saltmarsh is controlled by the (i) supply of colonists and (ii) attraction to under-exploited organic matter and that any relic fauna exerts little influence on the early stages of the colonisation process.