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A 134-d bioassay using sublethal quantities of zinc was conducted beginning with 5-d-old guppies, Poecilia reticulata. Five-day-old control fry had the highest whole body zinc concentrations (mg/g) which declined with growth; the zinc burden (mg/fish) increased primarily from 56 to 70 d during the onset of pregnancy. Uptake of zinc following zinc exposure occurred during logarithmic growth and pregnancy indicating that females actively transfer zinc to the embryo; 0.328 mg/L zinc triggered an apparent excretion process. Guppies exposed to 0.173 mg/L zinc for 70 d had significantly greater zinc body concentrations than controls. Acute sensitivity to zinc was correlated with the zinc body concentration. Growth in wet weight remained uniform for 28 d; however, after 134 d 0.607 mg/L zinc reduced the wet weight of females by 40%. The most sensitive indicator of toxicity was sexual maturity, after 70 d at 0.173 mg/L zinc, significantly fewer females had matured. At 0.607 mg/L zinc, fewer females (50%) gave birth and the time until birth of the first brood increased. Equal growth in wet weight of the second generation fry occurred at all zinc concentrations with growth in both generations being statistically equal implying that the second-generation guppies had become acclimated to zinc exposure. An application factor ranging from 0.030 to 0.099 was calculated. Comparison of growth, reproductive, and body concentration/burden data suggests that at least two modes of zinc regulation exist among fishes.Key words: zinc, bioaccumulation, growth, sexual maturity, reproduction, guppy, application factor

An alternative fluorescence-based method has been developed for the direct detection of small quantities of DNA in solution. In this system, a serine protease (elastase) is coupled to a DNA oligonucleotide through a disulfide linkage. A bis-(tetraalanine)-derivatized rhodamine molecule BZTAlaR) has been synthesized for use as a substrate. BZTAlaR is nonfluorescent in its derivatized form and shows negligible hydrolysis in solution. Cleavage of the tetraalanyl groups from the rhodamine portion of the molecule restores its fluorescence. Hybridization of the elastase-oligonucleotide conjugate to its target, capture of the conjugate-target complex with streptavidin-coated magnetic beads, addition of substrate, and subsequent detection of the target by fluorescence are accomplished in solution. Hybridization is rapid and specific, with over 90% of a target sequence successfully hybridized and captured. This method exhibits low background and an amplified fluorescent signal over time, resulting in a current detection limit of 0.49 fmol of elastase alone, or 2.64 fmol of conjugate, within 2 h.

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