Chronic Effects of Low Dissolved Oxygen Concentrations on the Fathead Minnow (Pimephales promelas)

Fathead minnows were exposed to constant dissolved oxygen concentrations (1.0–5.0 mg/liter) for 11 months. The number of eggs produced per female was reduced at 2.0 mg/liter; no spawning occurred at 1.0 mg/liter. Fry growth was reduced significantly at all concentrations below the control (7.9 mg/liter). Fry survival was reduced at 4.0 mg/liter and lower dissolved oxygen concentrations; 18% of the survivors at 4.0 mg/liter were deformed. The time required for hatching was increased at successively lower oxygen concentrations by as much as 50% (from 5.0 under control conditions to 7.8 days at 2.0 mg/liter), but no effect on percentage hatch was observed.