Salinity-dependent nickel accumulation and effects on respiration, ion regulation and oxidative stress in the galaxiid fish, Galaxias maculatus

Inanga (Galaxias maculatus) are a euryhaline and amphidromous Southern hemisphere fish species inhabiting waters highly contaminated in trace elements such as nickel (Ni). Ni is known to exert its toxic effects on aquatic biota via three key mechanisms: inhibition of respiration, impaired ion regulation, and stimulation of oxidative stress. Inanga acclimated to freshwater (FW), 50% seawater (SW) or 100% SW were exposed to 0, 150 or 2000 μg Ni L⁻¹, and tissue Ni accumulation, metabolic rate, ion regulation (tissue ions, calcium (Ca) ion influx), and oxidative stress (catalase activity, protein carbonylation) were measured after 96 h. Ni accumulation increased with Ni exposure concentration in gill, gut and remaining body, but not in liver. Only in the gill was Ni accumulation affected by exposure salinity, with lower branchial Ni burdens in 100% and 50% SW inanga, relative to FW fish. There were no Ni-dependent effects on respiration, or Ca influx, and the only Ni-dependent effect on tissue ion content was on gill potassium. Catalase activity and protein carbonylation were affected by Ni, primarily in FW, but only at 150 μg Ni L⁻¹. Salinity therefore offsets the effects of Ni, despite minimal changes in Ni bioavailability. These data suggest only minor effects of Ni in inanga, even at highly elevated environmental Ni concentrations. - Highlights: • Nickel (Ni) accumulation and toxicity was examined in the amphidromous fish, inanga. • Ni accumulation was tissue-, salinity-, and concentration-dependent. • Exposure to Ni concentrations as high as 2000 μg L⁻¹ had only minor effects on inanga. • Catalase activity and protein carbonylation were the most affected end-points. • Salinity protects against Ni toxicity, likely owing to changes in physiology. - Even at elevated environmental concentrations, nickel has only minor sub-lethal impacts in the widely-distributed Southern hemisphere fish Galaxias maculatus, with effects largely restricted to freshwater settings.