Page 972 - The Toxicology of Fishes

952 The Toxicology of Fishes

FIGURE 24.4 Examples of mesocosm systems used to assess the effects of pulp and paper effluents on fish.

replicate streams after long-term exposures, species use limitations for some designs, and logistical
difficulties (e.g., no access to power or reference water).

Caging Studies
Until recently, caging studies have not been recommended for measuring PME effects on fish because
the effects of the effluent could not be isolated from effects due to confinement stress (Environment
Canada, 1997b); however, in a number of situations caging of fish has been used successfully to document
exposure and to document the characteristics of biochemical responses to exposure (Birtwell et al., 1998;
McMaster et al., 1996b; Munkittrick et al., 1999; Parrott et al., 2000b) (Table 24.4). For example, Birtwell
et al. (1998) held juvenile Pacific salmon in 50-L net cages placed adjacent to the effluent discharges
from coastal pulp mills in British Columbia, Canada, to assess effluent effects on survival. In these
experiments, survival of fish was related to exposure to the effluent of the mill and related variables.
Confinement of juvenile salmon did not affect short-term (4- to 12-day) survival at reference sites;
therefore, caging studies should be considered as an alternative for short-duration exposures of small-
bodied species or juveniles and in field situations where effluent exposure is well defined. Caging studies
have also had some applications in conducting short-term exposures used to investigate the causes of
field effects (see Bioaccumulation Model section below).