Page 968 - The Toxicology of Fishes

948 The Toxicology of Fishes

Indicators of Reproductive Function
Reproductive success in fish depends on successful courtship, mating, egg development, hatching, and
growth of larvae and juveniles under suitable environmental conditions (Donaldson, 1990). Regulation
of reproductive endocrine function is essential to ensure reproductive success under varying environ-
mental conditions and to maintain internal homeostasis. Interruptions or changes to the control mecha-
nisms of the hypothalamic–pituitary–gonadal axis of fish have the potential to alter individual
reproductive capability or fitness at the best (e.g., reduced gonad growth and hormone metabolism) and
alter population viability at the worst (e.g., reduced fecundity, abundance) (Arcand-Hoy and Benson,
1998; Donaldson, 1990). Exposure to some chemicals (endocrine-disrupting compounds, or EDCcs) are
thought to alter reproductive function by mimicking natural hormones, inhibiting the action of hormones,
and/or altering the normal regulatory function of the endocrine system (Cooper and Kavlock, 1997;
Crisp et al., 1998). Changes to biological indicators of reproductive success have been used in fish to
assess effects of PMEs. Exposure to effluent has reduced gonad size, fecundity, and gamete size; increased
age at sexual maturation; depressed levels of reproductive steroid hormones; and altered expression of
secondary sex characteristics (Andersson et al., 1988; Leblanc et al., 1997; McMaster et al., 1991, 1992;
Munkittrick et al., 1991, 1992a,b, 1994; Sandström et al., 1988). Although these effects are believed to
be caused by compounds that interfere with the maintenance of normal reproductive endocrine homeo-
stasis in fish (Crisp et al., 1998; Van Der Kraak et al., 1992, 1998), the mechanisms of reproductive
endocrine dysfunction with PME exposure are poorly understood. Van Der Kraak et al. (1992) have
shown that exposure of white sucker to BKPMEs affected reproductive endocrine communication at
several sites within the hypothalamic–pituitary–gonadal axis, including gonadotropin production and
ovarian steroidogenesis; however, correlations between indicators of reproductive health and with other
fish health indicators are not consistent, resulting in the ecological relevance of these indicators being
questioned (Kovacs, 1986; Kovacs et al., 1997). In addition, not all PMEs cause changes in indicators
of fish reproduction (Swanson et al., 1994, 1996). At the present time, indicators of reproductive health
in fish continue to be monitored to assess PME effects. Although the ecological relevance of these
indicators may be questioned, a change does represent an alteration in normal reproductive-endocrine
function (Arcand-Hoy and Benson, 1998), and this has the potential for population-level effects neces-
sitating continued measurement of these indicators.

Monitoring Approaches
Ecological Field Assessments
Field assessments are used to establish baseline environmental conditions prior to the discharge of PME
or, more commonly, to determine if an existing discharge is affecting biota. Conducting studies in the
field is the most environmentally relevant approach to assessing effects under real-life conditions com-
pared to other approaches such as laboratory toxicity tests or artificial stream studies. One approach
used to assess the effects of PMEs is to examine areas exposed to effluent and determine whether there
are changes in the organisms living there. This approach has been used extensively to assess pulp and
paper effects on fish (Table 24.1). Typically fish are collected from a series of reference sites to determine
the normal variability in health under unexposed conditions. Organisms are also collected from effluent-
exposed areas at increasing distances from the PME discharge. The health of fish in these collections is
then compared among sites to determine if exposed fish are different, the magnitude of the difference
relative to natural variability at reference sites, and if the health improves with distance from the
discharge. One of the greatest challenges in any assessment program is determining if changes due to
a particular stressor (e.g., PMEs) are outside of what could be expected due to natural variability alone.
Comparison of indicators between reference and exposure sites is an approach that attempts to tease out
stressor-induced variability (e.g., PMEs) from natural variability (e.g., individual differences in a pop-
ulation of unexposed fish).
Several assumptions are associated with conducting ecological field assessments to measure pulp and
paper effects, including: (1) the sites sampled differ only in exposure to effluent (i.e., habitat differences
do not exist); (2) adequate reference sites exist for comparison; (3) organisms are present and abundant