Precautions for the Use of Copper Sulfate in Aquaculture

Copper sulfate solution has strong bactericidal properties and is commonly used for fish baths, disinfection of fishing gear (such as feeding sites), and prevention and treatment of fish diseases. However, due to the lack of understanding of the scientific use of copper sulfate among some aquaculture practitioners, the cure rate of fish diseases is low, and medication accidents may occur, leading to severe losses. This article focuses on the precautions for using copper sulfate in aquaculture.

1.Accurate Measurement of Water Body Area

Generally, when the concentration of copper sulfate is below 0.2 grams per cubic meter, it is ineffective against fish parasites; however, if the concentration exceeds 1 gram per cubic meter, it may cause fish poisoning and death. Therefore, when using copper sulfate, it is crucial to accurately measure the water body area and precisely calculate the dosage.

 2.Medication Precautions

(1) Copper sulfate is easily soluble in water, but its solubility in cold water is poor, so it needs to be dissolved in warm water. However, the water temperature should not exceed 60°C, as higher temperatures can cause the copper sulfate to lose its efficacy.

(2) The medication should be administered in the morning on sunny days and should not be applied immediately after soybean milk has been dispersed in the pond.

(3) When using in combination, copper sulfate should be paired with ferrous sulfate. Ferrous sulfate can enhance the permeability and astringency of the medication. Copper sulfate or ferrous sulfate alone cannot effectively kill parasites. The concentration of the combined solution should be 0.7 grams per cubic meter, with a ratio of 5:2 between copper sulfate and ferrous sulfate, i.e., 0.5 grams per cubic meter of copper sulfate and 0.2 grams per cubic meter of ferrous sulfate.

(4) Preventing oxygen depletion: When using copper sulfate to kill algae, the decomposition of dead algae can consume a large amount of oxygen, which may lead to oxygen depletion in the pond. Therefore, close monitoring is required after medication. If fish show signs of suffocation or other abnormalities, immediate measures such as adding fresh water or using oxygenation equipment should be taken.

(5) Targeted medication: Copper sulfate can be used to prevent and treat fish diseases caused by certain algae, such as infections caused by Hematodinium spp. and filamentous algae (e.g., Spirogyra), as well as Ichthyophthirius multifiliis, ciliates, and Daphnia infections. However, not all diseases caused by algae and parasites can be treated with copper sulfate. For instance, copper sulfate should not be used for Ichthyophthirius infections, as it may not kill the parasite and might even cause its proliferation. In ponds with infections caused by Hematodinium, copper sulfate can increase water acidity, stimulate algae growth, and worsen the condition.

3.Prohibitions for Copper Sulfate Use

(1) Copper sulfate should be avoided for use with scaleless fish, as they are sensitive to the compound.

(2) It is best not to use copper sulfate in hot and humid weather, as its toxicity is closely related to water temperature—the higher the water temperature, the stronger the toxicity.

(3) When the water is lean and has high transparency, the dosage of copper sulfate should be appropriately reduced because its toxicity is stronger in water with low organic matter.

(4) When using copper sulfate to kill large quantities of cyanobacteria, do not apply it all at once. Instead, apply it in small amounts multiple times, as the rapid decay of large amounts of algae can severely deteriorate water quality and even lead to oxygen depletion or poisoning.