SYSTEMATIC ANALYSIS OF AQUEOUS ION REQUIREMENTS OF HYALELLA-AZTECA - A STANDARD ARTIFICIAL MEDIUM INCLUDING THE ESSENTIAL BROMIDE ION

Sodium and bicarbonate are essential ions required by Hyalella azteca; their absence results in rapid mortality. Calcium and bromide are the only other two aqueous ions needed for long-term (10-week) survival w hen cotton gauze is present as a substrate and Tetra-Min fish food fla kes are used as food. Calcium and bromide act synergistically; neither ion by itself improves survival, and high calcium concentrations may even be toxic in the absence of bromide. Magnesium and potassium impro ve growth, and potassium improves production of Live young. Magnesium is toxic in the absence of calcium. Sulphate and chloride are not need ed; either anion can be used when making up media with salts of the es sential cations. A standard five-salt artificial medium is suitable fo r long-term experiments and culture of Hyalella, permitting standardiz ed testing over time and among laboratories. Ionic composition, especi ally sodium and bromide, may limit the natural distribution of Hyalell a and should be checked before attributing the absence of amphipods to pollutant effects.