POSTEMBRYONIC GROWTH AND DEVELOPMENT OF HYALELLA-AZTECA IN LABORATORYCULTURES AND CONTAMINATED SEDIMENTS

The environmental, biological, and ecological requirements of but a fe w species used in testing sediments are known and well understood. The present investigation was designed to provide fundamental information on the postembryonic growth and development of Hyalella azteca (Amphi poda) that can be used as sublethal indicators of contaminated sedimen ts, and the influence growth characteristics may have on interpretatio n of sediment toxicity test results. The biological endpoints for meas uring H. azteca growth and development included sexual maturation, mol t frequency, intermolt duration, body length, antennal segment additio n, and the relation between total body length and antennal segment add ition. To use growth and development of H. azteca as sublethal indicat ors of contaminated sediments, tests of up to 28 days duration should begin with immature amphipods (less than two weeks old) that will begi n the adult stage at the end of the test. Sexual maturation begins at the sixth instar (about 24 days at 20 degrees C) and can be used as a sublethal indicator of development effects. The presence of an enlarge d propodus is a reliable indicator of sexual maturation in H. azteca w hich easily distinguishes the immature (first five instars) from the j uvenile (instars 6 and 7) stage.