EGG VIABILITY AND ECOLOGY OF DEVILS HOLE PUPFISH - INSIGHTS FROM CAPTIVE PROPAGATION

Our efforts to develop techniques to rear Devils Hole pupfish, Cyprino don diabolis, in captivity led to a better understanding of ecological relationships in the natural habitat. Fish from autumn and spring col lections were allowed to spawn in laboratory aquaria. Those collected in spring produced five times more eggs. Spawns yielded one individual from an autumn collection and two from a spring collection that survi ved to adulthood. The extreme low egg viability experienced under labo ratory conditions probably occurs differentially over the spawning hab itat in nature. Shallow areas supporting algae populations that produc e substantial diel variation in oxygen saturation produce most larvae. Larval production declines as diel oxygen variation declines. Through out the deeper waters, the relatively constant oxygen saturation of ab out 40% is probably lethal to eggs. Population expansion in nature may also be limited by adult predation on larvae. High mortality of eggs and larvae may be important life history characteristics that help kee p the population within carrying capacity in a habitat that does not a llow emigration. Individual pupfish probably spawn during a single per iod of their lifetime of approximately one year. These life history ch aracteristics apparently limit the potential of artificial propagation as a reliable recovery tool. Our experiences with captive propagation and analyses of data from Devil's Hole lead to the following conclusi ons regarding management of refugia. Since constant conditions of oxyg en saturation may not be optimal, refugium populations should be provi ded with spawning substrates in areas where algae populations produce diel variation in oxygen concentrations. Escape cover for larvae seems essential. The relationship between diel variation in oxygen, tempera ture, and hatching success requires further examination.