Sub-lethal exposure encompasses a range of negative effects that may disrupt ecological balance and food web dynamics beyond mere mortality. Even non-fatal injuries may have long-term consequences for a species' fitness and survival if they lead to changes in behavior, decreased reproductive success, or heightened vulnerability to predators. Stress certainly contributed to a decrease in locomotor activity, as evaluated by both distance traveled and swimming speed, in fish exposed to 60 Ag/L (1/5 of LC50). Accumulation of acetylcholine (ACh), a neurotransmitter at synaptic synapses, and the subsequent alteration in locomotor behavior may result from either the decrease of AChE enzyme activity (40-55% in the brain) or the bioaccumulation of the toxicant in other parts of fish. Chlorpyrifos has the highest bioaccumulation values in the viscera, followed by the brain and the remainder of the body. Chlorpyrifos residues in food and water sources increase worries about long-term, low-dose exposure and its potential health consequences on humans.
Key words: Chlorpyrifos, Sub-lethal, Locomotor, Acetylcholine, Enzyme.