Showing papers in "Fish Physiology in 2011"

An introduction to metals in fish physiology and toxicology: basic principles

Abstract: A brief history of metals, their early investigation in fish by physiologists and toxicologists, and current terminology are presented The conceptual basis for the topics explored in each of the metal-specific chapters of these two volumes is then described These include sources of metals, their economic importance, environmental situations of concern, essentiality or non-essentiality, bioconcentration or lack thereof, and the overarching importance of chemical speciation in understanding their effects on fish The techniques used to derive ambient water quality criteria for metals are explained Key mechanisms of acute and chronic toxicity are reviewed, as well as recent findings on the mechanisms and sites of uptake, internal handling, biotransformation, subcellular partitioning, detoxification, storage, and excretion Important new research fronts focus on behavioral effects, molecular and omic analyses of cellular responses, and the effects of interacting metals in fish Similarities and differences among the metals dealt with in these volumes are highlighted

Molybdenum and chromium

Abstract: Molybdenum (Mo) and chromium (Cr) both exist in elevated concentrations in aquatic environments primarily as oxyanions: molybdate (MoO42−) and chromate (CrO42−). These concentrations typically arise as a result of anthropogenic activity. Both metals are relatively non-toxic compared to other metals. Average 96 h LC50 estimates in freshwater are at least 1000 mg L−1 for Mo and approximately 100 mg L−1 for Cr. Both metals are micronutrients, but there is no evidence that their internal concentrations in animals are regulated in a homeostatic manner. Molybdenum is involved in purine metabolism, and Cr is involved in fat and glucose metabolism. Very little information exists about the physiological impact of elevated aquatic concentrations of these metals, especially Mo, in fish. Chromium is taken up by the gills and distributed via the blood to a variety of tissues but the mechanism of uptake across the gills is unknown. Chromium's toxic mechanism in fish is unknown, but histopathologies, particularly of the gastrointestinal tract and kidney, play a significant role in its toxicity. Molybdenum is also transported across the gills via an unknown mechanism and accumulates internally in the liver; other sites of accumulation have not been identified. The speculation on toxicity of Mo includes a non-specific gill irritation response, but this lacks experimental evidence. The general metabolism of these two metals in fish and the factors that influence their bioavailability need future investigation, and provide limitless opportunities for future research.

Field studies on metal accumulation and effects in fish

Abstract: Metals have been present in the environment since the origin of our planet. Life has evolved in their presence, incorporating many of them in essential molecules and metabolic processes and developing protective mechanisms against both non-essential metals and excess essential metals. Anthropogenic metal contamination of terrestrial and aquatic systems dates as far back as the first traces of human civilization. However, it was not until the intense industrialization of the eighteenth century that severe environmental impacts of metal mining and smelting activities started to pose a serious threat to wildlife. Field research leading to environmental protection legislation first appeared for mercury and selenium, owing to their propensity to biomagnify and cause toxicity to the higher levels of food webs such as birds and humans. However, we have only recently started to reveal the mechanisms of metal accumulation and toxicity on fish and other wildlife for low-level, chronic exposure scenarios. In aquatic environments, fish accumulate metals via both aqueous and dietary routes. The effects of chronic metal exposure, typical of most metal-contaminated environments, are more subtle than, and greatly differ from, the effects of acute exposures. There is evidence of direct toxicity leading to bioenergetic consequences such as decreased growth rate and condition, as well as selective pressures reducing population genetic diversity. Direct metal toxicity at other trophic levels also induces indirect effects, both negative and positive, on fish populations. Because metal accumulation and toxicity in wild fish are affected by several biotic and abiotic factors, field modeling remains a challenge. Nevertheless, with the advancement of knowledge, reviewed in this chapter, on accumulation and effects of metals in wild fish, our capacity to protect fish and their habitat from anthropogenic metal contamination is fast improving.

Modeling the Physiology and Toxicology of Metals

Abstract: Most bioaccumulation models in current use were originally developed for organic chemicals and subsequently applied to metals. As a result, they do not typically incorporate metal-specific features that affect how metals are taken up, metabolized, detoxified, and eliminated. This review describes models that are used to evaluate metal accumulation, from waterborne and dietary exposure, by aquatic organisms. It considers whole-body models (including single-compartment and multicompartment variations), physiologically based pharmacokinetic models (providing an explicit representation of individual organs), and food chain or food web models. A representative model framework and example application are described for each model. Variations are also discussed. Metal bioaccumulation models have not typically been developed to predict effects on aquatic organisms. However, several that were developed for this purpose are described herein. These include damage–repair models, biotic ligand models, physiologically based mechanistic models, and intracellular speciation models. While some effects models incorporate relatively unique metal-specific features, they have primarily been applied to waterborne exposures, and received limited use for predicting effects resulting from both waterborne and dietary exposures. Studies that facilitate the refinement of both bioaccumulation and effects models, and the unification of such models, will likely benefit both the scientific and regulatory communities.