Laserfiche WebLink
<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 <br />