The use of nanoparticulate silver (AgNP) is increasingly widespread and recently has been shown to have a plausible release route into aquatic environments. To date, relatively little research has examined the effects of AgNP on estuarine fish. The authors present data indicating that chronic exposure to low levels of AgNP induces significant adverse effects in both juvenile and adult sheepshead minnows (Cyprinodon variegarus; SHMs). Chronic exposure to low levels of AgNP produced significant increases in tissue burdens in both juvenile and adult SHMs, resulting in significant thickening of epithelia gill tissue and in dramatically altered gene expression profiles. The results do not appear to be attributable to the release of silver ions through particle dissolution. The alteration in gene expression was greatest in adult gonads, but no evidence of AgNP-related dysfunction was found at the tissue level. In contrast, the authors found a significant effect on gill morphology, but very little evidence of effect on gill transcription profiles.

Cyclic changes in dissolved oxygen occur naturally in shallow estuarine systems, yet little is known about the adaptations and responses of estuarine organisms to cyclic hypoxia. Here we examine the responses of Palaemonetes pugio, a species of grass shrimp, to cyclic hypoxia (1.5-8 mg/l dissolved oxygen; 4.20-22.42 kPa) at both the molecular and organismal levels. We measured alterations in gene expression in hepatopancreas tissue of female grass shrimp using custom cDNA macroarrays. After short-term (3-d) exposure to cyclic hypoxia, mitochondrial manganese superoxide dismutase (MnSOD) was upregulated and 70-kd heat shock proteins (HSP70) were downregulated. After 7-d exposure, nuclear genes encoding mitochondrial proteins (ribosomal protein S2, ATP synthase, very-long-chain specific acyl-CoA dehydrogenase [VLCAD]) were downregulated, whereas mitochondrial phosphoenol pyruvate carboxykinase (PEP Cbk) was upregulated. After 14 d, vitellogenin and apolipoprotein A1 were upregulated. Taken together, these changes suggest a shift in metabolism toward gluconeogenesis and lipid export. Long-term (77-d) exposure to hypoxia showed that profiles of gene expression returned to pre-exposure levels. These molecular responses differ markedly from those induced by chronic hypoxia. At the organismal level, cyclic hypoxia reduces the number of broods and eggs a female can produce. Demographic analysis showed a lower estimated rate of population growth in grass shrimp exposed to both continuous and short-term cyclic hypoxia, suggesting population-level impacts on grass shrimp.

We report the construction of a genome-wide fish metabolic network model, MetaFishNet, and its application to analyzing high throughput gene expression data. This model is a stepping stone to broader applications of fish systems biology, for example by guiding study design through comparison with human metabolism and the integration of multiple data types. MetaFishNet resources, including a pathway enrichment analysis tool, are accessible at http://metafishnet.appspot.com.

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A need exists for whole animal toxicity, mutagenesis, and carcinogenesis models that are alternative to the traditional rodent test models and that are economical, sensitive, and scientifically acceptable. Among small fish models, the Japanese medaka (Oryzias latipes) is preeminent for investigating effects of carcinogenic and/or toxic waterborne hazards to humans. The guppy (Poecilia reticulata), although less widely used, is valuable as a comparison species. Both species are easy to maintain and handle in the laboratory and there is a large body of background information on their responsiveness to a range of classes of carcinogens. There are considerable data on the occurrence of background diseases and on spontaneous neoplastic lesions, both of which occur relatively rarely. With few modifications, the medaka and guppy are amenable to carcinogenicity testing under the rigid standards established by the National Toxicology Program (NTP) for rodent tests. The advantages of the small fish in carcinogenesis studies are best realized in long-term studies that involve environmentally realistic exposures. Studies to identify chronic effects can be conducted in about 12 months, near the life span of medaka in our laboratory. Practically, 9-month studies are optimal but shorter study cycles and a variety of exposure/growout and initiation/promotion scenarios are available. Studies on 3 compounds tested in medaka under NTP protocols are under review and preliminary analysis indicates that chronic carcinogenicity bioassays with medaka, guppy, and potentially with other small fish species are feasible and scientifically valid.