Copper use and accumulation in catfish culture in the Mekong Delta, Vietnam

Abstract

Aquaculture of Pangasius hypophthalmus (striped catfish) in Vietnam reached 1.1 million tonnes in 2011 and catfish fillets are exported worldwide. The intensive cultures of catfish mainly in earth ponds have made it necessary to apply CuSO₄ and other chemicals to control external parasites and other pathogens. However, accumulation of Cu in aquaculture ponds may pose a hazard to growth of fish or to the aquatic environment. The aim of this study was to determine accumulation of Cu in sediment, water and fish in a catfish pond with a history of repeated treatment with CuSO₄ in the Mekong Delta, Vietnam. Copper concentrations in pond sediment were in the interval 21.3–45.7 mg kg⁻¹ dw and did not exceed the Vietnamese values for soil to be used for agricultural production (70 mg kg⁻¹ dw.). During three samplings the total mean concentration of Cu in pond water (4 μg L⁻¹) did not exceed the LC₅₀-value (70 μg L⁻¹) for catfish and the mean dissolved concentration of Cu (0.986 μg L⁻¹) did not seem to constitute a risk for the stability of the aquatic ecosystem. No significant variation in Cu concentrations between sampling sites in the pond and depth of sediment profile were determined. The accumulation of Cu in catfish was highest in the liver compared to the skin, gills and muscle tissue. With the current practice of removing pond sludge three to four times during a production cycle little if any Cu seems to accumulate in catfish ponds despite repeated anti-parasite treatments with CuSO₄. Further studies are needed to assess the eco-toxicity and impact on agricultural production when pond sediment is discharged into aquatic recipients and used as soil fertilizer.

Keywords:

• Toxic element
• fish pond
• sediment
• copper sulphate
• aquaculture
• channel catfish

Acknowledgment

Dr. Vo Nam Son and staff at the College of Aquaculture and Fisheries at the University of Can Tho, Vietnam is thanked for their support during the stay of Helle Løjmand in Vietnam, especially the staff working on the EU-supported FP7 project “Sustaining Ethical Aquaculture Trade” (SEAT; project contract no. 222889; www.seatglobal.eu) who provided logistical and other support for the study. The catfish farmer is thanked for providing access to the farm and help collecting the samples from the pond and answering questions regarding the management of his farm.