Lethal Effects of Elevated pH and Ammonia on Early Life Stages of Hybrid Striped Bass

Abstract

Hybrid striped bass larvae (striped bass, Morone saxatilis, ♀ x white bass, M. chrysops, ♂) are often stocked into fertile culture ponds. High rates of photosynthesis may result in elevated pH which can be lethal to fry and can affect the toxicity of ammonia. Six-hour static toxicity tests were performed on hybrid larvae of various ages to determine the toxicity of elevated pH and the effects of elevated pH on ammonia toxicity. Six-hour mortality threshold pH's with no measurable ammonia were estimated for various age larvae and found to be between pH's 9.8 and 10.2 for D2 (Dl is day of hatch), between 9.0 and 9.4 for D4, between 8.8 and 9.2 for D13, and between 9.2 and 9.4 for D20 fish. The addition of 0.7% NaCl had no effect on the toxicity of elevated pH to D2 or D4 fish but caused a significant reduction in the mortality of Dl3 and D20 fish exposed to high pH. The tolerance to elevated pH decreased as ammonia concentration increased. Sub-lethal un-ionized ammonia concentrations increased the toxicity of elevated pH, suggesting an interaction of pH and un-ionized ammonia toxicity.