EFFECT OF CALCIUM AND MAGNESIUM HARDNESS ON ACUTE COPPER TOXICITY TO CATFISH.

ALERT...
The article published by S. Adhikari (2003, abstract below left),
Aquaculture Research, 34(12): 975, directly copied the article written by
Perschbacher and Wurts (1999, abstract below right) and the discussion from
Wurts and Perschbacher (1994, abstract below right).

Articles copied:
Effects of calcium and magnesium hardness on acute copper toxicity to juvenile channel catfish Ictalurus punctatus. Aquaculture, 172: 275-280. Perschbacher, P. W. and W. A. Wurts. 1999.

Effects of bicarbonate alkalinity and calcium on the acute toxicity of copper to juvenile channel catfish (Ictalurus punctatus). Aquaculture, 125: 73-79. Wurts, W. A. and P. W. Perschbacher. 1994.

Article by S. Adhikari:

Effect of calcium and magnesium hardness on acute copper toxicity to Indian major carp, Labeo rohita (Hamilton) and catfish, Channa punctatus (Bloch)

Abstract
Four experiments were conducted to evaluate the effects of calcium and magnesium hardness on the acute toxicity of copper sulphate to Indian major carp, rohu (Labeo rohita, Hamilton) fingerlings and juvenile catfish (Channa punctatus, Bloch) in medium alkalinity experiments. A preliminary bioassay determined the 96 h LC50 of copper sulphate to be 0.56 mg/L  for L. rohita fingerlings and 11.78 mg/L  for juvenile C. punctatus placed in water with calcium hardness and total alkalinity set at 100 mg/L  CaCO3. In the first experiment, rohu were exposed to 0.56 mg/L  copper sulphate in environments where calcium hardness was varied from 50 to 350 mg/L  CaCO3 and total alkalinity was 100 mg/L  CaCO3. As calcium hardness increased, copper-induced rohu mortalities decreased significantly from 90% at 50 mg/L  CaCO3 to 7% at 350 mg/L  CaCO3. In the second experiment, rohu were exposed to 0.56 mg/L  copper sulphate in environments where magnesium hardness was varied from 50 to 350 mg/L  CaCO3 with total alkalinity set at 100 mg/L  CaCO3. Hundred percent mortality was observed in magnesium-based hardness treatments. In the third experiment, catfish were exposed to 11.78 mg/L  copper sulphate in environments where calcium hardness was varied from 50 to 400 mg/L  and total alkalinity was 100 mg/L  CaCO3. As calcium hardness increased, copper-induced catfish mortalities decreased significantly from 90% at 50 mg/L  CaCO3 to 4% at 400 mg/L  CaCO3. In the fourth experiment, catfish were exposed to 11.78 mg/L  copper sulphate in environments where magnesium hardness was varied from 50 to 400 mg/L  CaCO3, with total alkalinity set at 100 mg/L  CaCO3. In this case, 100% mortality was also observed in magnesium-based treatments. Mortality rates in magnesium hardness treatments were consistent with those in the second experiment. These data suggest a calcium-specific mechanism with respect to acute copper toxicity both in rohu and catfish.

KEYWORDS:
copper, toxicity, calcium, magnesium, alkalinity, catfish, fish

For reprints of the original articles by Pershcbacher and Wurts (1999) and Wurts and Perschbacher (1994) click on the following links:

Effects of calcium and magnesium hardness on acute copper toxicity to juvenile channel catfish Ictalurus punctatus. Aquaculture, 172: 275-280. Perschbacher, P. W. and W. A. Wurts. 1999.

Effects of bicarbonate alkalinity and calcium on the acute toxicity of copper to juvenile channel catfish (Ictalurus punctatus). Aquaculture, 125: 73-79. Wurts, W. A. and P. W. Perschbacher. 1994.

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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 for juvenile catfish placed in water with calcium hardness and total alkalinity set at 20 mg/L CaCO3. In the first experiment, catfish were exposed to 1.25 mg/L copper sulfate in environments where calcium hardness was varied from 10-400 mg/L CaCO3. Total alkalinity was 20 mg/L CaCO3. As calcium hardness increased, copper-induced catfish mortalities decreased significantly from 90% at 10 mg/L CaCO3 to 5% at 400 mg/L CaCO3. In the second experiment, catfish were exposed to 1.25 mg/L copper sulfate in environments containing either calcium or magnesium hardness, 20 and 400 mg/L CaCO3, with total alkalinity set at 20 mg/L 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.

Article by Wurts and Pershcbacher (1994):

Effects of bicarbonate alkalinity and calcium on the acute toxicity of copper to juvenile channel catfish (Ictalurus punctatus)

Abstract
Three experiments were conducted to evaluate the relative importance of calcium hardness and bicarbonate alkalinity to the acute response of juvenile channel catfish (Ictalurus punctatus) exposed to a toxic concentration of copper sulfate. A preliminary bioassay revealed 28 mg/L copper sulfate caused 50% mortality within 48 h (48-h LC50) in juvenile channel catfish placed in water with calcium hardness and bicarbonate alkalinity, set at 75 mg/L CaC03. Catfish were then exposed to 28 mg/L copper sulfate concentrations in environments where hardness or alkalinity concentrations were varied. Bicarbonate alkalinities above 75 mg/L CaC03, with calcium hardness held at 20 mg/L CaC03, significantly reduced catfish mortalities from 97-100% to 63-70%. Copper-induced mortalities were 100% for all fish placed in calcium hardness treatments (20-250 mg/L CaC03) in which bicarbonate alkalinity was held at 20 mg/L CaC03. When bicarbonate alkalinity was held constant at 75 mg/L CaC03 and calcium hardness was varied from 20 to 250 mg/L CaC03, copper related catfish mortalities displayed high variability and means ranged from 6.7 to 60%. Mortalities decreased as calcium concentrations increased. Although differences in mortalities were not statistically significant, the latter hardness findings appear to suggest a biologically significant calcium effect on copper toxicity in the presence of sufficient alkalinity concentrations.