Chronic effects of low ph and elevated aluminum on survival, maturation, spawning and embryo-larval development of the fathead minnow in soft water

Abstract

Fathead minnows (Pimephales promelas) were exposed to a range of pH and A1 concentrations in soft water (8 mg Ca L⁻¹) to determine effect levels at various life stages. The tested pH levels ranged from 8.0 through 5.2 and inorganic monomeric Al from 15 through 60 μg L⁻¹. Reproductive processes including spawning, embryogenesis and early larval survival were more sensitive to acid stress than were juvenile growth and survival. Juvenile survival was significantly reduced at pH 5.2 + 60 μg Al L⁻¹ (P <0.05). Spawning success was reduced at pH 6.0 and 5.5 (P <0.10) and failed completely at pH 5.2, regardless of Al concentration. An apparant beneficial effect of added Al was observed during spawning at pH 7.5 + 35 μg Al L⁻¹, but this effect was not significantly greater than at pH 7.5 + 15 μg Al L⁻¹. A significant (P <0.05) decrease in larval survival occurred at pH 6.0 + 15 μg Al L⁻¹ and lower compared to the survival at pH 7.5 + 15 μg Al L⁻¹. Aluminum at 30 μg L⁻¹ provided protection resulting in short term increased embryo-larval survival at pH 5.5. The effect of parental exposure on progeny survival was assessed by an interchange of embryos from the spawning treatment to all tested exposure conditions. When reared at pH 8.0 + 15 μg Al L⁻¹ through 6.0 + 15 μg Al L⁻¹ or at pH 5.5 + 30 μg Al L⁻¹, parental exposure did not significantly influence progeny survival. However, survival was significantly reduced among progeny from brood fish reared at pH 5.5 + 15 μg Al L⁻¹ as compared to those spawned at pH 6.0 + 15 μg Al L⁻¹ and above, or at pH 5.5 + 30 μg Al L⁻¹ (P <0.05). Juvenile or 14 d larval growth effects were not detected under any exposure condition (P >0.05). Ultimately, fathead minnow young-of-the-year recruitment and production potential can be expected to diminish when environmental pH falls to 6.0, and to fail completely at 5.5 and lower.