Aquaculture
172 (1999) 275-280
Short
communication
Effects of calcium
and magnesium hardness on acute copper toxicity to juvenile channel catfish Ictalurus punctatus
Peter W.
Perschbachera and William A. Wurtsb,*
aAquaculture and
Fisheries Center, Box 4912, University of Arkansas at Pine Bluff, Pine Bluff,
AR 71611, USA
bCooperative
Extension Program, Kentucky
State University P.O. Box 469 , Princeton , KY 42445-0469 , USA
Accepted 19 November 1998
________________________________________________________________________
Abstract
Two experiments were conducted to
evaluate the effects of calcium or magnesium hardness on the acute toxicity of
copper sulfate to juvenile channel catfish (Ictalurus punctatus) in low
alkalinity environments. A preliminary
bioassay determined the 48-h LC50 of copper sulfate to be 1.25 mg l-1
for juvenile catfish placed in water with calcium hardness and total alkalinity
set at 20 mg l-1 CaCO3.
In the first experiment, catfish were exposed to 1.25 mg l-1
copper sulfate in environments where calcium hardness was varied from 10-400 mg
l-1 CaCO3. Total
alkalinity was 20 mg l-1 CaCO3. As calcium hardness increased, copper-induced
catfish mortalities decreased significantly from 90% at 10 mg l-1 CaCO3
to 5% at 400 mg l-1 CaCO3. In the second experiment, catfish were
exposed to 1.25 mg l-1 copper sulfate in environments containing
either calcium or magnesium hardness, 20 and 400 mg l-1 CaCO3,
with total alkalinity set at 20 mg l-1 CaCO3. Survivals in calcium hardness treatments were
consistent with those in the first experiment.
However, 100% mortality was observed in both treatments containing
magnesium-based hardness. These data
suggest a calcium-specific mechanism with respect to acute copper toxicity in
channel catfish. © 1999 Elsevier Science B.V.
All rights reserved.
Keywords:
copper, toxicity, calcium, magnesium, fish
______________________________________________________________________________
1.
Introduction
Copper sulfate is
routinely used as an algicide in commercial and recreational fish ponds. It has also been used as an effective
treatment for pathogenic protozoan parasites of fish.
It is generally recognized that copper
can be highly toxic to teleosts. However,
several studies have reported that either calcium hardness or alkalinity
concentrations have significant effects on copper toxicity. Therefore, recommendations for safe use of
copper sulfate have been based on hardness (Inglis and Davis, 1972; Post, 1983;
Sawyer et al., 1989) and total alkalinity concentrations of water (MacMillan,
1985; Wellborn, 1985; Reardon and Harrell, 1990).
Straus
and Tucker (1993) reported that total alkalinity and total hardness had
significant effects on acute copper toxicity to juvenile channel catfish (Ictalurus punctatus). Wurts and Perschbacher (1994) observed that
alkalinity concentration had the most pronounced effect on acute copper
toxicity to juvenile channel catfish when calcium hardness and alkalinity
concentrations were treated as independent variables. Wurts and Perschbacher (1994) also reported a
calcium hardness effect, which could affect channel catfish tolerance to copper
toxicity in low alkalinity environments.
Miller and Mackay (1980) believed calcium hardness was more important
than alkalinity in protecting fish from copper toxicity, based on experiments
with juvenile rainbow trout (Oncorhynchus mykiss). Research about fathead minnows (Pimephales
promelas) and rainbow trout, however, found no significant calcium effect on
copper uptake sites (Lauren and McDonald, 1987a; Playle et al., 1993a; Zia and
McDonald, 1994). Furthermore, it has
been proposed that magnesium hardness also competes with copper for binding
sites on the gills (Playle et al., 1993b).
The
present study determined whether acute copper toxicity to juvenile channel
catfish was affected by increasing calcium hardness concentrations in low
alkalinity waters. Then by substituting
magnesium for calcium at equal hardness concentrations, it was possible to
compare the effects of magnesium versus calcium on the acute toxicity of copper
to juvenile channel catfish.
2.
Methods
Two
bioassays were conducted to facilitate evaluations about calcium and magnesium
effects on acute copper toxicity. The
first bioassay determined the amount of copper sulfate needed to effect a 48-h
LC50 for 7-10 g juvenile channel catfish in water with calcium
hardness and total alkalinity concentrations set at 20 mg l-1 CaCO3. The second bioassay examined whether 48-h
survival would be adversely affected if juvenile channel catfish were placed in
calcium-free water with high magnesium concentrations and no copper added. Techniques followed EPA guidelines (U.S.
Environmental Protection Agency, 1975).
Experiments
were conducted to evaluate the mortality response of juvenile channel catfish
exposed to a potentially toxic concentration of copper sulfate in waters with
differing concentrations of calcium or magnesium hardness and a constant low
alkalinity concentration. Two trials
were conducted: one varied calcium hardness and the other varied calcium or
magnesium hardness. Each combination of
hardness and alkalinity was replicated in four, aerated, 7.6-l aquaria. Each aquarium was stocked with seven juvenile
channel catfish. Length and weight
averages for catfish were 102 + 5.2 mm and 8.2±0.9g.
Trial
1 involved exposing fish to 1.25 mg l-1 copper sulfate in
environments with five different concentrations of calcium hardness, ranging
from 10 to 400 mg l-1. Total
alkalinity was held constant at 20 mg l-1. Catfish were also observed in a control
environment where calcium hardness was 400 mg l-1 CaCO3
and total alkalinity was 20 mg l-1 CaCO3, and no copper
was added.
Trial
2 examined the relative effects on copper toxicity (1.25 mg l-1
copper sulfate) of magnesium versus calcium hardness at concentrations of 20
and 400 mg l-1 CaCO3.
Total alkalinity was held constant at 20 mg L-1 CaCO3.
Methods used to
create and test water treatments, copper toxicity and water quality were the
same as those reported by Wurts and Perschbacher (1994). Magnesium hardness was adjusted to desired
concentrations with reagent grade magnesium sulfate.
Fish were not fed
48 h prior to or during each experiment.
Catfish were held for 24 h preceding each experiment in a holding tank
with water containing calcium hardness and total alkalinity, set at 20 mg l-1
CaCO3. Water temperature,
dissolved oxygen, ammonia-nitrogen (NH3-N) and pH were measured to
monitor water quality. Mortalities were
removed and totaled at regular intervals.
Survival
data were analyzed using PROC GLM
and Fischer's LSD (Ott, 1977; SAS, 1989).
Percentile data were transformed using the arc-sine method suggested by
Mostellar and Youtz (1961). Significance
was tested at the 0.05 level.
3.
Results and Discussion
A
copper sulfate concentration of 1.25 mg l -1 was required to effect
a 48-h LC50 for juvenile channel catfish placed in water containing
total alkalinity and calcium hardness set at 20 mg l-1 CaCO3. Water temperature was 21.5º C.
After 48 h,
survival was 100% for juvenile catfish placed in aquaria containing
calcium-free water with a magnesium hardness of 400 mg l-1 CaCO3.
It
is interesting to note that the copper concentration producing 48-hr LC50
in this study, 1.25 mg l-1 copper sulfate at low alkalinity (20 mg l-1
CaCO3), was substantially lower than that reported by Wurts and
Perschbacher (1994) for water of moderate alkalinity (i.e. 28 mg l-1
CuSO4, at 75 mg l-1 CaCO3). At a low alkalinity concentration, much less
copper was required to produce acute toxicity.
In
general, water quality was poorest in aquaria with the highest survivals
(Tables 1 and 2). Water temperatures
ranged from 22.6-23.8ºC in trial 1 and 21.7-22.3ºC in trial 2. Mean total NH3-N concentrations
ranged from 1.4-1.6 mg l-1 at 2 h and 2.9-4.0 mg l-1 at
42 h in the first experiment. Mean pH
ranged from 6.6-7.0 in trial 1 and 6.5-6.9 in trial 2. Mean dissolved oxygen concentrations ranged
from 4.8-6.4 mg l-1 in trial 1 and 5.0-7.5 mg l-1 in
trial 2.
In
one aquarium each, from trial 1 and trial 2, disruption of aeration occurred
for several hours; and two fish jumped from one aquarium in trial 1. Survival data from these aquaria were treated
as missing data in the statistical analyses.
In
trial 1, there were significant differences among experimental groups with
respect to survival and calcium hardness concentrations. As calcium hardness increased, catfish survival
improved significantly from 10% at 10 mg l-1 CaCO3 to 95%
at 400 mg l-1
Table 1
Mean 48-h survivals and water quality
data for juvenile channel catfish exposed to 1.25 mg l-1 copper
sulfate at varying calcium hardness concentrations with total alkalinity held
constant at 20 mg l-1 CaCO3
|
|||||
Hardness
(mg l-1)
|
42-h
pH
|
42-h
NH3-N (mg l-1)
|
DO
|
Survivala
(%)
|
|
2-h
(mg l-1)
|
18-h
(mg l-1)
|
||||
10b
|
7.0
|
2.9
|
5.5
|
5.8
|
10w
|
20
|
6.8
|
3.2
|
5.3
|
5.7
|
32w
|
50
|
6.8
|
3.7
|
5.6
|
6.1
|
71x
|
200
|
6.8
|
3.9
|
5.1
|
5.1
|
93x,y
|
400b
|
6.9
|
3.9
|
5.7
|
5.6
|
95y
|
400c
(control)
|
6.7
|
4.0
|
5.3
|
4.8
|
100y
|
a
Values
followed by the same superscript were not significantly different at the 0.05
level.
b
Means
for survival, pH and NH3-N within these rows were based on three
values rather than four because fish either jumped from or aeration was
disrupted in one tank after 18-h.
c
The
control was not exposed to copper sulfate.
|
|||||
CaCO3 (Table 1). Survival was 100% in the control. Mean survivals (93 and 95%) at 200 and 400 mg
l-1 calcium hardness were not significantly different from one
another or from 100 % survival in the control.
The data indicate a calcium hardness between 50 and 200 mg l-1
would reduce toxicity and mortality for juvenile channel catfish exposed to a
copper sulfate concentration of 1.25 mg l-1, where total alkalinity
is 20 mg l-1 CaCO3.
In
trial 2, 100% was mortality in both treatments containing magnesium-based hardness,
20 and 400 mg l-1 CaCO3.
Survivals were 48 and 100% in 20 and 400 mg l-1 calcium
hardness treatments, respectively, and were consistent with those in trial 1
(Tables 1 and 2).
These
data suggest a calcium-specific mechanism with respect to acute copper toxicity
in juvenile channel catfish. There is convincing
evidence to suggest that copper
Table 2
Mean 48-h survivals and water quality
data for juvenile channel catfish exposed to 1.25 mg l-1 copper
sulfate at varying calcium or magnesium hardness concentrations with total
alkalinity held constant at 20 mg l-1 CaCO3
|
||||
Hardness
(mg l-1)
|
pH
|
DO
|
Survivala
(%)
|
|
2-h
(mg l-1)
|
18-h
(mg l-1)
|
|||
Calcium
|
||||
20b
|
6.5
|
6.3
|
5.0
|
48x
|
400
|
6.7
|
6.4
|
5.3
|
100w
|
Magnesium
|
||||
20
|
6.7
|
6.4
|
5.7
|
0y
|
400
|
6.8
|
6.5
|
6.6
|
0y
|
a
Values
followed by the same superscript were not significantly different at the 0.05
level.
b
Mean
survival within this row was based on three values rather than four because
aeration was disrupted after 18-h in one tank.
|
disrupts ion homeostasis (Lewis and
Lewis,1971; Lauren and McDonald, 1986, 1987b; Reid and McDonald, 1988) and that
environmental calcium directly affects osmoregulation, in teleosts (Potts and
Flemming, 1971; Bournancin et al., 1972; Flemming et al., 1974; Eddy,1975;
Evans, 1975; Isaia and Masoni, 1976; McWilliams and Potts, 1978; Pic and Maetz,
1981). Indeed, it seems plausible that
copper competitively inhibits calcium binding sites, such as those associated
with calcium activated channels for monovalent ions (Perez et al., 1994;
Vambutas et al., 1994; Levitan and Rogowski, 1996). Inhibition or suppression of osmoregulatory
mechanisms would result in critical losses of serum electrolytes; which in
turn, could cause tetany, cardiovascular failure and death. As observed in this study, a high ratio of
the concentrations of calcium to copper ions would minimize the toxic effects
of copper (by reducing or preventing competitive inhibition).
The
present research substantiates reports that indicate calcium hardness affects
copper toxicity in teleosts. Calcium
hardness significantly affected survival of juvenile channel catfish exposed to
a toxic concentration of copper sulfate in low alkalinity water. But, magnesium hardness provided no
protection from copper toxicity. This
study emphasizes the importance of measuring calcium hardness before using
copper sulfate in waters with low alkalinity concentrations.
Acknowledgments
We
gratefully acknowledge Dwight Wolfe for his valuable assistance with
statistical analyses and UAPB student intern, Lloyd Inman, for assistance with
the experimental trials. We thank
Forrest Wynne and Drs. Andrew Goodwin, Bob Durborow, Rebecca Lochmann and
Michael Masser for reviewing this manuscript.
This manuscript was assigned publication number 97141 by the Arkansas
Agricultural Experiment Station.
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