Environmentally Realistic Levels of Total Suspended Solids Damage Gill Structure and Compromise Swimming Performance...

Total suspended solids (TSS) have been shown to damage the structural integrity of fish gills, impairing their function, including gas exchange. However, studies showing linkages between gill damage due to TSS and fish performance are limited. There is a large diversity of fish species inhabiting aquatic environments, and whether the TSS impact on gill function is similar across a range of species has yet to be explored. Here, we exposed multiple species, including salmonids (rainbow, brook and cutthroat trout) and cyprinids (fathead minnow and longnose dace) to a range of TSS concentrations (0-1000 mg L^-1) for 4 d and assessed damages to gill structure (filament thickness, lamellae thickness, oxygen diffusion distance, lamellae length, epithelial lifting, and interlamellar distance) using confocal microscopy. All species tested showed similar gill structural damage, including thicker lamellae, longer oxygen diffusion distances, and reduced respiratory surface area, at concentrations ≥ 100 mg L^-1 TSS. To assess whether gill damage corresponds to performance dysfunction, we tested the metabolic rate and swimming capacity of a salmonid (rainbow trout) and a cyprinid (fathead minnow) after exposure to 100 mg L^-1 TSS using swim tunnel respirometry. Trout showed lower routine metabolic rate (RMR) and maximum metabolic rate (MMR) after TSS exposure and were unable to reach the higher swimming speeds attained by unexposed fish. Fathead minnows showed no difference in the RMR after TSS exposure, but, like trout, had a lower MMR and were unable to attain the higher swimming speed of the control fish. Both species showed a ~35% reduction in the critical swimming speed (U_crit). These findings reveal that environmentally realistic TSS concentrations damage gill structure, impair fish swimming performance, and may compromise their ability to cope with energy-demanding activities, including additional biotic and abiotic stressors.