<br />found to affect every aspect of the feeding sequence,
<br />including detection of prey, prey capture, handling time,
<br />ingestion of prey, and general motivation to feed (Little
<br />et a!., 1993). The reduced growth in razorback sucker
<br />and bony tail in the 8X and 16X treatments was proba-
<br />bly due in part to reduced feeding activity.
<br />Little and Finger (1990) reported that swimming
<br />behavior is a sensitive indicator of some contaminant
<br />stresses, but not others. They reviewed the literature
<br />and concluded that swimming activity measured as
<br />changes in water column position, swimming posture,
<br />body movements, or swimming pattern, were more sen-
<br />sitive to contaminant stresses than was swimming ca-
<br />pacity, which reflects the ability of a fish to swim
<br />against sustained or incrementally increasing velocities
<br />of water. They found that adverse effects on swimming
<br />behavior often occurred at 0.1-5% of the LC 50' but for
<br />certain chemicals effects did not occur until lethal
<br />concentrations were present. In our study, adverse ef-
<br />fects on swimming performance occurred in the same
<br />treatments where reduced survival and growth were
<br />observed. These results are similar to Waiwood and
<br />Beamish (1978) who reported that critical swimming
<br />performance of rainbow trout exposed to copper was
<br />reduced only at concentrations approaching the lethal
<br />threshold at high hardness and pH.
<br />Cleveland et aI. (1993) reported that at exposures of
<br />680 to 2700 J.Lg/L of selenium, bluegill exhibited al-
<br />tered swimming behavior including lethargic, abnormal
<br />swimming postures and confinement to aquaria bot-
<br />toms, and reduced the frequency or duration of swim-
<br />ming movements, but there was no consistent effects
<br />on feeding, aggression, coloration, or responsiveness to
<br />external stimulation. Their lowest test concentration
<br />with adverse effects was over 2 times greater than the
<br />250 J.Lg/L threshold concentration for selenium found
<br />by Weir and Hine (1970) for conditioned learning in
<br />goldfish (Carassius auratus). Zinc concentrations as low
<br />as 100 J.Lg/L have altered locomotion activity in bluegill
<br />(Ellgaard et al., 1978). Zinc has also been shown to
<br />reduce the ability of the minnow Phoxinus phoxinus to
<br />compensate for torque in a rotating water current at
<br />concentrations as low as 60 J.Lg/L (Bengtsson, 1974a).
<br />Thus, copper, selenium, and zinc have been found to
<br />alter swimming behavior at concentrations within the
<br />range of those tested in the present study.
<br />The consequences of altered behaviors such as re-
<br />duced swimming ability are increased vulnerability to
<br />predation, lessened chance of encountering prey by
<br />reduced search areas, and disruption of essential func-
<br />tions such as habitat selection, or competition, or re-
<br />production through the loss of a population or changes
<br />in year-class strength when enough individuals are af-
<br />fected (Little et aI., 1993).
<br />
<br />SIMULATING IRRIGATION WATER TOXICITY 59
<br />
<br />Growth, Survival, and Residues
<br />
<br />Selenium probably contributed the majority of the toxic
<br />effects observed on growth and survival in the present
<br />study because selenium concentrations in the IX and
<br />2X treatments were similar to those causing adverse
<br />effects in other species. Three other waterborne studies
<br />with selenium have shown adverse effects on survival
<br />and growth of rainbow trout and chinook salmon
<br />(Oncorhynchus tshawytscha) after 60 days exposure to
<br />47 to 142 J.Lg/L (Hamilton et aI., 1986; Hamilton and
<br />Wiedmeyer, 1990; Hunn et aI., 1987). In these studies,
<br />fish in the lowest treatments with adverse effects had
<br />whole-body residues of selenium ranging from 3.8 to
<br />5.2 J.Lg/ g. In a waterborne selenium exposure of bluegill
<br />to 680 J.Lg/L and higher, reduced survival and altered
<br />behavior were associated with whole-body residues of
<br />4.3 to 5.1 J.Lg/g (Cleveland et a!., 1993). Waterborne
<br />concentrations of selenium and whole-body residues in
<br />these five studies are equal to or less than the concen-
<br />trations in the present study where adverse effects on
<br />survival (480-1232 J.Lg/L) and growth (;;.. 252 J.Lg/L)
<br />occurred. In the present study, adverse effects in razor-
<br />back sucker were associated with whole-body concen-
<br />trations of 5.9 to 7.6 J.Lg/g and in the bonytail study at
<br />9.4 to 10.8 J.Lg/g.
<br />In two selenium dietary studies with chinook salmon,
<br />whole-body residues of selenium of 4.0 to 6.5 /J-g/ g
<br />were associated with reduced survival and growth
<br />(Hamilton et aI., 1990). In a selenium dietary study with
<br />bluegill, whole-body residues of 4.2 to 4.3 /J-g/g were
<br />associated with reduced survival (Cleveland et aI., 1993).
<br />This convergence of adverse effects from waterborne
<br />and dietary exposures with a variety of fish species
<br />suggests that once selenium residues reach a certain
<br />threshold, regardless of the route of exposure, adverse
<br />effects will occur. This supposition is supported by the
<br />results of a study by Hodson et aI. (1980) where rain-
<br />bow trout were exposed to 53 /J-g/L of selenium for
<br />308 days, which should have caused adverse effects,
<br />based on exposure concentration and exposure dura-
<br />tion. Yet, no effects were observed on survival, growth,
<br />condition factor, or several blood and plasma measure-
<br />ments. In their study, whole-body residues of selenium
<br />were 1.8 /J-g/g (assuming 75% moisture, reported as
<br />0.44 /J-g/ g wet wt.), which is substantially below the
<br />toxic threshold of 4-6 J.Lg/ g mentioned above. Thus,
<br />based on whole-body residues, no adverse would have
<br />been expected in their study.
<br />Exposure to copper concentrations of 37 /J-g/L in
<br />the razorback sucker study (4X) and 67 p.g/L in the
<br />bony tail study (8X) could have also contributed to the
<br />reduced growth and survival observed in the present
<br />study. Seim et aI. (1984) reported that growth was
<br />reduced in steelhead trout exposed either continuously
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