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.

Background: Lake Diatas is one of the important lake which is influenced by agricultural activities around the lake, and chlorpyrifos is widely used as a pesticide in this area. This study aimed to analyze the damage of the gill tissue of Oreochromis niloticus L. and Cyprinus carpio L. as two freshwater fish, which are mostly caught to be consumed by the residents in Lake Diatas, Indonesia, that were exposed to chlorpyrifos.
Methods: Acclimatization was performed for 14 days and continued with toxicity test for 30 days. Chlorpyrifos exposure was tested at various concentrations. Fish gill tissue was observed microscopically in 10, 20, and 30 days of exposure, and damages were scored based on the level of gill tissue damage.
Results: It was revealed that O. niloticus L. experienced edema, proximal basal hyperplasia, fusion, hyperplasia in all secondary lamellae, and necrosis at the higher exposure concentration. While C. carpio L. experienced fusion, hyperplasia, clubbing, necrosis, and obvious degradation of gill tissue of fish after 30 days of exposure to chlorpyrifos. There was a significant difference in the damage of fish gill tissue between each variation treatment (P < 0.05).
Conclusion: According to the results, the higher the concentration of chlorpyrifos and the longer the exposure time, the higher the level of damage in gill tissue.