Increased metabolic demand reveals morpho-functional impacts caused by settleable atmospheric particulate matter on fish gills

Exposure to environmentally relevant levels of settleable atmospheric particulate matter (SePM) limits the aerobic performance of inactive healthy adult fish. We evaluated the gill morpho-functional impacts (gill structure and ionic balance) caused by SePM exposure (96 h) in Nile tilapia when fish is impelled to maximal aerobic swimming effort. In control fish, swimming reduced epithelial filament thickness (EFT, 25 %), increased the distance between lamellae (DL, 21 %), and reduced the plasma Na⁺ (5 %). In resting fish, SePM exposure increased EFT (11 %), reduced DL (30 %), lamellar height (LH, 18 %), and plasma Na⁺ (4 %), whereas increased Cl^- and K⁺ (8 % and 20 %). In SePM-exposure fish, swimming reduced EFT (40 %), increased DL (30 %) and LH (30 %), while reduced Na⁺ and Cl^- (9 % and 18 %), and increased K⁺ when compared to inactive SePM-exposed fish. These morpho-functional limitations may compromise whole-body maintenance and swimming recovery, affecting the fish ability to perform at higher activity levels.