Page 723 - The Toxicology of Fishes

Biomarkers 703

effects) (Brown et al., 2004a; Eales and Brown 2005). Again, it is essential to have background infor-
mation on the seasonal, species/strain, metabolic, and reproductive status effects, as well as the influence
of general environmental conditions on blood hormone levels, so the effects of pollution can be separated
from this background variability.

Condition Indices

Physical condition indices have been used for many years in aquaculture as a simple method for
monitoring changes in fish health. These approaches index the physical dimensions of the animal or one
of its internal organs (e.g., liver, spleen, gonads) with body weight. The most common morphometric
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index is the condition factor, expressed as weight (g)/length (cm); however, organosomatic indices
(ratios of organ mass to body mass) may provide more specific information sometimes relating to the
function of the organ selected. Condition indices are also potentially very attractive biomarkers for field
biologists because they are simple to perform, often requiring little more than a battery-operated balance
and a ruler. The external measurements, such as the condition factor, are also of interest because they
are nondestructive and noninvasive. Condition indices, like many other biomarkers, are influenced by
environmental factors (e.g., season, temperature) (Imsland et al., 1995; Khallaf et al., 2003; Mustafa et
al., 1991) and the physiological status of the animal (e.g., nutrition) (Russell et al., 1996). Thus, temporal
changes in these indices may not be directly related to pollutant exposure. On the other hand, pollutants
can produce rapid and marked changes in condition indices that are clearly differentiated from any
underlying seasonal or life-cycle influence (e.g., in gonads) (Jobling et al., 1996). Goede and Barton
(1990) reviewed condition indices and described how the indices may be scored as part of a quantitative
autopsy technique, with obvious applications in aquaculture and aquatic toxicology. Attempts have also
been made to correlate multiple sets of indices (e.g., weight, length, organ weights) to measure fish
health at polluted and clean sites (see Table 16.6). This section briefly reviews the effects of pollutants
on condition indices and highlights some of the compounding factors worth considering in field and
laboratory studies. Some recent examples of the use of such indices in pollution studies are illustrated
in Table 16.6.

Condition Factor
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The condition factor relates body length to weight (weight/length ). This measurement is common in
fisheries and aquaculture because it is simple to perform; consequently, a growing body of literature
relates the common environmental stresses in fisheries, such as stocking density (Wagner et al., 1997),
dissolved oxygen (Miller et al., 1995), salinity (Craig et al., 1995), and food intake (Einen et al., 1998),
to the condition factor. These stresses decrease the condition factor, which is often interpreted as a
decline in body fat or stored glycogen in the liver. Similarly, pollutants that cause an increase in metabolic
rate, a decline in energy intake, or enhance fat metabolism as part of the mode of toxic action, are likely
to decrease condition factor (Smolders et al., 2003). Elevation of metabolic rate is a common response
to pollutant exposure (Randall et al., 1996), and many pollutants cause a decline in energy intake either
by changing feeding behavior (Little et al., 1985) or by toxic effects on absorption in the gastrointestinal
tract (Clearwater et al., 2005; Handy et al., 2005). These factors in combination with lipid peroxidation
of food items or the gut mucosa can cause a decline in condition factor.
Goede and Barton (1990) pointed out that, in wild fish populations, temperature, food availability,
competition, and other factors may interact synergistically to produce a general decline in fish health.
It may not be possible to elucidate pollutant effects on condition factor because the effects of pollutants
on the condition factor are masked by other biotic or abiotic variables. Pollutants may therefore decrease
the condition factor or have no apparent effect (see Table 16.6). In a study of the health and condition
of the Pacific herring (Clupea pallasi) after the Exxon Valdez oil spill, Elston et al. (1997) concluded
that the effects of reproductive stage, spawning behavior, and location were likely to invalidate inter-
pretation of condition indices data. In a study of the metal contamination in the Clark Fork River in
Montana (Farag et al., 1995), brown trout showed larger variation in the condition factor between
reference sites (0.93 to 0.41) compared to that between contaminated sites (0.46 to 0.31); however, in