MCHM (4-methylcyclohexane Methanol) Influences the Predator-Prey Interaction Between Danio Rerio and Daphnia Magna

Chemical contamination alters organism-level traits, such as activity and feeding, that can ultimately affect aquatic trophic interactions. Despite the importance of predator-prey relationships in aquatic communities, chemical toxicity is often tested on single species prior to use. For example, 4-methylcyclohexane methanol (MCHM) used in industrial coal-cleaning enters the environment regularly from low-level contamination during disposal and occasionally in high concentrations following accidental spills, but its effects on fish-zooplankton interactions remain unknown. It was hypothesized MCHM exposure affects zebrafish and D. magna swimming behavior differently when exposed individually or together, and ultimately affects their relationship. Zebrafish and D. magna were exposed individually and together to various environmentally relevant concentrations of MCHM. In the single-species experiments, zebrafish and D. magna swimming distance, velocity, and activity, as well as D. magna mortality, were quantified 1, 3, 5, and 7 days post-exposure to 0, 0.5, 1, 3, or 5 ppm MCHM. In single species tests, zebrafish in all MCHM treatments experienced an immediate and consistent decrease in all measured parameters. Daphnia magna swimming distance, velocity and activity also decreased by approximately 30-50%; however, unlike the zebrafish, mortality occurred after 3 days, reaching 100% by the end of the experiment. When exposed together, D. magna exhibited similar results to the individual test. In contrast, only zebrafish in the 1 and 5 ppm concentrations experienced decreased swimming distance and velocity when prey was present. To examine how decreased mobility in both organisms affected their predator-prey interaction, a feeding study was conducted. Zebrafish were exposed to MCHM concentrations of 0, 0.5, 1, 3, or 5 ppm. After 1, 3, 5, and 7 days, 15 live D. magna were released into a tank containing one fish. The number of D. magna remaining after 30 minutes and one hour was used to calculate feeding rate. The number of strikes performed by each zebrafish was also quantified. Zebrafish feeding rate decreased by 40% in the 1, 3 and 5 ppm MCHM treatments compared to the control throughout the exposure period. Zebrafish in those MCHM treatments also performed more strikes per D. magna consumed. The individual species tests suggest MCHM exposures longer than three days could lead to loss of zebrafish food resources. Short-term exposures led to decreased mobility in both organisms, and the feeding study results indicated these changes altered the zebrafish-D. magna predator-prey relationship