Abstract:
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.
