Background: The most commonly used insecticide by 99.8% farmers in West Sumatra, is chlorpyrifos which contains organophosphates. Chlorpyrifos is used to kill insects and other pests and works as the contact poison, gastric toxins, and inhalation. It is very useful for farmers in keeping the plants such
as corn, citrus, peanuts, and so forth. Chlorpyrifos can enter the water body with direct application to control pests or indirectly through either spraying or washing during high rainfall in spray applications for plant leaves. Chlorpyrifos is also used in farming in the region of Twin Lakes (Diatas Lake and
Dibawah Lake), West Sumatra, Indonesia. One of the most important fish that is cultivated in this region is Nile tilapia (Oreochromis niloticus).
Methods: The acute toxicity (LC50-96 h) of chlorpyrifos for Nile tilapia in studies was 0.076 mg/L. Sublethal concentrations used for the studies were one-seventh (0.011 mg/L) and one-fourteenth (0.005 mg/L) of the LC50-96 h. The test animal was exposed to the both sublethal concentrations for
1, 7 and 14 days. Behavioral responses were studied in the experimental periods. Tilapia that exposed chlorpyrifos exposure was exhibited irregular body movements, gills and fins motion, mucus secretion, breathing at the surface, and anal excretion.
Results: It was revealed that the longer the exposure time, the more visible behavioral changes in fish, as well as the concentration variations, it means that the higher the concentration, the more visible changes in physiological behavior of fish. Correlation values (R) were was 0.75–0.99.
Conclusion: These behavioral responses can be used as a tool in biomonitoring program to monitor ecotoxicity risk of chlorpyrifos to the test species, especially in the region of Twin Lakes, West Sumatra, Indonesia.