Dietary Exposure to Environmentally Relevant Levels of Chemical Contaminants Reduces Growth and Survival in Juvenile Chinook Salmon

Abstract

Chemical pollution can degrade aquatic ecosystems. Chinook salmon in contaminated habitats are vulnerable to health impacts from toxic exposures. Few studies have been conducted on adverse health outcomes associated with current levels and mixtures of contaminants. Fewer still address effects specific to the juvenile life-stage of salmonids. The present study evaluated contaminant-related effects from dietary exposure to environmentally relevant concentrations and mixture profiles in juvenile Chinook salmon from industrialized waterways in the U.S. Pacific Northwest using two end points: growth assessment and disease susceptibility. The dose and chemical proportions were reconstituted based on environmental sampling and analysis using the stomach contents of juvenile Chinook salmon recently collected from contaminated, industrialized waterways. Groups of fish were fed a mixture with fixed proportions of 10 polychlorinated biphenyls (PCBs), 3 dichlorodiphenyltrichloroethanes (DDTs), and 13 polycyclic aromatic hydrocarbons (PAHs) at five concentrations for 35 days. These contaminant compounds were selected because of elevated concentrations and the widespread presence in sediments throughout industrialized waterways. Fork length and otolith microstructural growth indicators were significantly reduced in fish fed environmentally relevant concentrations of these contaminants. In addition, contaminant-exposed Chinook salmon were more susceptible to disease during controlled challenges with the pathogen Aeromonas salmonicida. Our results indicate that dietary exposure to contaminants impairs growth and immune function in juvenile Chinook salmon, thereby highlighting that current environmental exposure to chemicals of potential management concern threatens the viability of exposed salmon.

Keywords: Chinook salmon; Natural Resource Damage Assessment (NRDA); dichlorodiphenyltrichloroethanes (DDTs); disease challenge; growth; persistent organic pollutants (POPs); polychlorinated biphenyls (PCBs); polycyclic aromatic hydrocarbons (PAHs).

Figure 1

Study design, flow of study, chronology of events, and outcomes measured.

Figure 2

Plots of predicted daily growth rate (otolith microns/day) by days fed the contaminated diet (days 4–35) visualized by treatment group with repeat measures of individual fish and tank as random effects; bands show 95% confidence intervals; *p < 0.05 overall growth rate across days 4–35 of receiving contaminated feed relative to the control group, +p < 0.05 growth rate with progressing days of the study (i.e., slope of growth curve) relative to the control group.

Figure 3

Forest plot of the hazard ratios (95% confidence interval) determined for each treatment (T1–T5) relative to the solvent control (SC) reference with a mixed effects Cox model of the salmon survival data. Hazard ratios greater than 1 indicate a greater risk of disease susceptibility during the challenge with Aeromonas salmonicida.