Effect of diethyl phthalate on predator–prey chemo-ecology in Lepidocephalichthys thermalis

Phthalates, an additive used in the plastics manufacturing industries, are also common pollutants in the aquatic environment. However, little is known about how phthalates affect chemo-recognition in fish controlling vital ecological decisions such as predator–prey cognition. Therefore, we investigated the effect of diethyl phthalate (DEP) on predator recognition mechanism using the common spiny loach, Lepidocephalichthys thermalis , as a model prey fish and dwarf snakehead, Channa gachua, as sympatric native predator. We also performed paired choice predation assay to evaluate if DEP exposure impacts prey survival in an actual predation event. Short-term exposure (STE) or Long-term exposure (LTE) to DEP followed by assessment of anti-predator responses using ethological assay clearly shows that DEP impairs innate predator recognition in common spiny loach. DEP-exposed prey fish did not recognize sympatric predator kairomones, alarm signals from conspecifics, and dietary cues from fed predators. The inability of DEP-exposed L. thermalis to distinguish conspecific alarm signals will likely to have an additional impact on associative learning, putting it at risk of predation by non-native predators. Anti-predatory responses of prey fish in LTE treatment groups were found to be more impacted than the STE treatment group. Furthermore, actual predation studies demonstrated that DEP-exposed L. thermalis had a lower survival rate than unexposed fishes, confirming that DEP exposure decrease survival in prey fish. Given the critical importance of chemically-mediated anti-predator strategies and associative learning ability to counter both native and non-native predators, ability of plasticizers to impose anti-predator behavioral suppression and reduce survival is likely to have long-term detrimental effects on fish fitness.