(03/11/1998) --- Dr. Dirk Voeste, a scientist with Ruhr-University of Bochum, Germany, examines some swordtail fish (Xiphophorus helleri), like those that are part of the Neurolab payload on Space Shuttle Mission STS-90, in their holding tank in the Operations and Checkout Building. The fish will fly in the Closed Equilibrated Biological Aquatic System (CEBAS) Minimodule, a middeck locker-sized fresh water habitat, designed to allow the controlled incubation of aquatic species in a self-stabilizing, artifical ecosystem for up to three weeks under space conditions. Investigations during the Neurolab mission will focus on the effects of microgravity on the nervous system. The crew of STS-90, slated for launch April 16 at 2:19 p.m. EDT, include Commander Richard Searfoss, Pilot Scott Altman, Mission Specialists Richard Linnehan, D.V.M., Dafydd (Dave) Williams, M.D., and Kathryn (Kay) Hire, and Payload Specialists Jay Buckey, M.D., and James Pawelczyk, Ph.D