Page 25 - The Toxicology of Fishes

Introduction 5

is nowhere near the total number of species, and for much of our current information we are dependent
on a relatively small fraction of the species.
Through the use of an expanding aquatic toxicology toolkit, effects of stressor chemicals on aquatic
organisms are being determined in an integrative manner on individuals and, in some instances, are
being extended to population and community levels of biological organization, as well. Most recently,
genomic approaches are being explored for their ability to reveal, for example, mechanisms of action,
differential sensitivities, and similarities and differences among organisms (see Chapter 5 in this volume).
Additionally, they may make substantial contributions to ecological risk assessments (Ankley et al.,
2006), as well as promote the integration of human health-oriented and ecologically oriented research
and policy (Benson and Di Giulio, 2006).
Why does one need to have a comprehensive treatment of the toxicology of fishes? Particularly with
regard to certain aspects of the subject in which enormous and recent growth has taken place, a great
deal of new information has been assembled and must be thoroughly reviewed to provide cohesive
coverage and to integrate new findings with existing concepts. The next set of challenges that investigators
may face in the field will likely cause additional attention to be drawn to organ, tissue, and cellular sites
that are being targeted and lead to approaches embodying likely different perspectives.
The Toxicology of Fishes is organized into four units. Unit I, “General Principles,” contains Chapters
1 through 6. Following this Introduction, Chapter 2 is devoted to the bioavailability of chemical con-
taminants in aquatic systems. To students new to this field, bioavailability is critical to our coverage
because certain forms of potentially toxic substances in water are bound to particulates in the aquatic
medium and are not available for uptake by fish. When uptake has occurred, distribution within the
individual fish must be considered, and this is the subject of Chapter 3, “Toxicokinetics in Fishes”; for
example, toxicokinetics permits us to understand the distribution within the individual and to approach
an improved quantitative estimate of the dose. The fourth chapter is concerned with biotransformations
in fishes and, among other things, covers the potential bioactivation of compounds into toxic forms and
their conjugation and removal. Chapter 5, “Molecular Mechanisms of Toxicity,” provides coverage of
the process by toxic states are achieved. Completing this first unit is an additional chapter on mechanisms,
particularly those arising through oxidative stress.
Unit II, “Key Target Systems and Organismal Effects,” is comprised of Chapters 7 through 13. Chapter
7, “Liver Toxicity,” covers the microscopic anatomy of the organ, important aspects of the liver physi-
ology in fishes, and morphological, biochemical, and functional aspects of toxic injury and its conse-
quences. Chapter 8, “The Osmoregulatory System,” covers the anatomy and physiology of the gill and
its perturbations by metals and other aquatic pollutants; given the extensive surface area and role in
uptake of contaminants, the osmoregulatory function of this organ may be compromised by exposure
to metals and selected organic compounds. Chapter 9, “Toxic Responses of the Fish Nervous System,”
provides a description of the central nervous system of fishes and describes a variety of toxic responses,
some morphological and others physiological. The coverage leads to improved understanding of the
nature of specific toxic induced alterations. Chapter 10, “The Endocrine System,” describes the endocrine
system of fishes and its toxicity, and receptor-mediated mechanisms and the effect of contaminants on
hormone function are covered in detail. Chapter 11 describes the immune system of fish, a known target
for certain toxicants that can directly affect the individual’s host defense mechanisms. How these toxic
responses arise and their significance are the subjects of this chapter. Chemical carcinogenesis of fishes
is the subject of Chapter 12, in which a brief history of this interesting aspect of chronic toxicity is
provided followed by coverage of molecular aspects of carcinogenesis. Discussions of procarcinogens
illustrate important information about fish as models. Both laboratory and field studies are reviewed,
and the various fishes that have been studied from contaminated and reference sites are presented. The
final chapter in this section, Chapter 13, is a treatment of toxicity resistance; it is important to understand
how animals including fishes can adapt to chemical contamination and the long-term consequences of
such adaptations.
Unit III, “Methodologies and Applications,” is an assemblage of five chapters. Chapter 14, “Exposure
Assessment and Modeling in the Aquatic Environment,” is followed by a chapter on fish toxicity studies
which reviews methods and approaches for determining acute and chronic toxicities in various laboratory
applications. Responses that indicate exposure, adverse effects, and genetic susceptibility are included