ARS - 2012

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    Acute Toxicity and Sub-lethal Effects of Chlorpyrifos to Three Larvivorous Fish, Poecilia eticulate Aplocheilus dayi, and Rasbora daniconius
    (University of Kelaniya, 2012) Ganehiarachchi, G.A.S.M.; Amarasinghe, L.D.; Weerasinghe, T.
    The insecticide belonging to the organophosphate group, chlorpyrifos 40 % EC, is reported to be highly toxic on fish and it is under restricted usage globally. This chemical is used by Dry Zone chena cultivators and hence, there is a possibility of contaminating the bordering water sources rich with larvivorous fish by tracer amounts of this chemical. Two naturally occurring fish species, Aplocheilus dayi (nalahandaya) and Rasbora daniconius (dandiya) and introduced fish species, Poecilia reticulata (wild guppy) are among the potential larvivorous fish in Sri Lanka. The present study was carried out to find out; acute toxicity of chlorpyrifos 40% EC (commando™), to Aplocheilus dayi, Rasbora daniconius and Poecilia reticulata, effects of sub-lethal concentrations of chlorpyrifos on offspring production and on histological alterations in the gill structure. The exposure media contained a series of concentrations (50, 5, 0.5 and 0 μg/l) of chlorpyrifos 40 EC in glass aquaria. Based on the mortality data, LC50 (24 hr) value of chlorpyrifos 40 EC for Aplocheilus dayi, Rasbora daniconius and Poeceilia reticulata was estimated as 0.514μg/l, 0.472 μg/l and 0.882μg/l respectively. It was also revealed that chlorpyrifos 0.5 μg/l of sub-lethal level to P. reticulata has induced production of hatchlings (mean number of 15 hatchings per female per day) whereas no production of hatchings was observed in other treatments during the exposure period. Histopathological study of the gills exposed to 5 and 50 μg/l of chlopyrifos for 48 hr showed hypertrophy of gill arches, lifting and degeneration of lamella epithelium, degeneration of gill filaments and vasodialation in the lamella axis of both Rasbora daniconius and Poecilia reticulata. This study concludes that LC50 values vary for three fish species tested and Poecilia reticulata is more resistant than the other two species. The sub-lethal levels of contaminants of chlorpyrifos 40EC cause histological and physiological aberration in freshwater fish.
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    Phytoplankton and Zooplankton Community Dynamics and Aspects of Food of Two Fish Species in Two Streams and Two Lakes in Presence and Absence of Anophelese Mosquito Larvae in Mahaoya, Sri Lanka
    (University of Kelaniya, 2012) Amarasinghe, L.D.; Ganehiarachchi, G.A.S.M.; Ruchirani, C.; Weerasinghe, T.
    Plankton samples were collected using plankton nets to examine the phytoplankton and zooplankton community dynamics in two streams: namely, Mahaoya, and Panajjawa Oya and two lakes: namely, Bubula Lake and Wagaspitiya Lake in Mahaoya, Ampara district, Sri Lanka. The samples were collected in two consecutive periods in May and August 2011. Aplocheilus dayi and Rasbora daniconius, two naturally occurring fish species were collected (n=50) using cast nets to examine their food aspects in absence of Anopheles mosquito larvae in May 2011 and in their presence in August 2011. Of the total plankton community, only about 28% (14 species) represented zooplanktons while 72% (55 species) were phytoplanktons. Total 14 zooplankton species belonged to; Class Branchiopoda (5 species); Class Lobosa (1 species); Class Maxillopoda (4 species); and Class Monogononta (4 species), and 55 species of phytoplankton population belonged to Class; Chlorophyta (24 species); Class Cyanophyta (11 species); Class Bacillariaphyta (10 species); Class Ochrophyta (4 species); Class Euglenophyta (4 species); Class Heterokontophyta (2 species). The zooplankton population of two streams was dominated by Chromogaster spp. (40 - 80 /ml) while that of two lakes, Bubula and Wagaspitiya were dominated by Eucyclops spp.(120/ml) and Cyclops spp. (80/ml) respectively. The phytoplankton population in all the four water bodies was dominated by Closterium spp. (200-400/ml). The above data reveals that the phytoplankton diversity in two lakes is greater (total of 26 species/taxa) than that of two streams (total number of 14 species/taxa) but, there was no difference in zooplankton diversity between the two habitats. Density and diversity of both phytoplankton and zooplankton in each site between two consecutive sampling occasions (soon after heavy rains in absence of mosquito larvae and during the dry spell in presence of mosquito larvae) did not vary significantly. Gut analysis of two naturally occurring fish species, Aplocheilus dayi and Rasbora daniconius revealed that both of their diets mainly composed of crustaceans 40%, insects 35% and algae, detritus, diatoms and plant parts 25% by number, in presence of mosquito larvae in the habitats in August 2011.