Advertisements by Google



Author: Dr. Panos Varvarigos
Freelance Veterinarian - Fish Pathologist, Athens, Greece.


Reproduction of this website (or parts of it) is illegal and strictly forbidden.
No rights can be derived from this website.



Poster presented at the 13th International EAFP conference on Fish and Shellfidh Diseases. 17th - 21st September 2007. Grado, Italy.


The origin of the problem:

Copper in sea-water, either in the form of bivalent cupric ion, copper hydroxide, carbonate complexes, oxides or as organic copper compounds, is a toxicant to marine life. In aquaculture, the antifouling products used to impregnate the cage netting contain 18-25% cuprous oxides.



The use of antifouling "paints" has increased in line with the proliferation of the large circular fish cages, which are necessary for expanding production and moving gradually to more wave exposed marine sites. However, their netting is heavy and frequent net changes are laborious and time consuming. Copper and copper oxides from the impregnated nets gradually dissolve in the sea-water prohibiting the establishment of algae and bivalves that foul the netting, thus prolonging the continuous use of the nets.





After about a year in the sea, the impregnated nets are washed on shore in net washer drums. The effluent from these often flows into the sea, either untreated or subsequent to some degree of sedimentation. Commonly, fresh net impregnation takes place near the shore creating spillage, which also finds its way into the sea with rainfall. As a result the copper content of the bottom sediments and of the sea-water is elevated and adversely affects fish health.


Susceptible farmed species, age/size:

All cultured species are susceptible; their sensitivity being size/age dependent. Smaller fish sufer the more accute consequences.

Empirical, personal observations over the recent years have concluded that sea bass (Dicentrarchus labrax) is much more sensitive than sea bream (Sparus auratus) to the presence of elevated copper levels in the water.

Main lesions and diagnosis:



Sub-lethal copper toxicity in fish relates to cell membrane permeability and osmoregulation, enzyme synthesis and function.



The skin darkens, thickens and appears fragile and ulcerated, in particular around the mouth. The fins are eroded. There is congestion of the meninges, which is evident through the thin and semi-transparent skull (meningitis ensues, particularly on young bass).




The gill epithelium is inflamed, thickened and degenerate; excessive mucus is secreted, gill function and resistance against parasite and bacteria establishment are compromised.



The liver and spleen appear pale and degenerate.


The red blood cells are intoxicated and their shape is disturbed. Typically, a large proportion of erythrocytes on fresh or fixed Giemsa stained blood smears appear elongated, spindle shaped or bent. Immature erythrocytes proliferate due to increased blood destruction and the affected fish become progressively anemic.



Such compromised fish are slow growers and become easy targets for common parasites. Gill trematodiases and bacterial gill disease unexpectedly become serious causes of fish losses. In pump-ashore nurseries young fry turn anorectic and lethargic, darken, emaciate and may die in numbers.


Toxicity depends on copper bioavailability, which is influenced in turn by water temperature and water movement re-suspending in the water column sediments rich in copper. Young age classes of fish are more sensitive, sea-bass being more susceptible than sea bream.

Sea water testing:

During the past twenty months, twenty five samples of surface sea-water among cages, tested with Atomic Absorption Spectroscopy, revealed total copper content from 0.43 to 23.2 μg/lt. (ppb), mean value of 5.53 ppb and standard deviation 5.61.


Half of the samples contained copper above 3ppb. Fourteen samples of sediments under the cages returned copper content values ranging between 2.85 and 221.20 mg/kg (ppm) with a mean value of 47.41 ppm and standard deviation 63.66. The U.S. Environmental Protection Agency considers copper at 2.9 μg/lt. sea-water as the "Criterion Maximum Concentration".

Economic Implications:

Covert but significant. Expected to intensify

Frequency of occurrence:



Costs associated with copper toxicity may comprise:

1. Increased mortality, especially among juveniles and fry.
2. Chronic stress and high propensity to infectious diseases (indirect mortality).
3. Growth retardation.

Environmental issues:

Increased copper levels in the water are toxic for all biota. Copper-based antifouling contamination of the marine environment must be prevented in view to sustaining coastal aquaculture.


No specific regulations are in place concerning upper limits for total copper concentration in bottom sediments or in sea-water. Regulations exist only as regards copper in potable water, hence there is some confusion.

Selected Bibliography:

Eleftheriadou, M. and Skoulos, M. (2004) Nutrient and trace metal distribution in the Gulf of Astakos, Aetoloakarnania, Greece. Global Nest: the Int. J. 5(3):117-124


Mourad, M. and Wahby, O. (1999) Physiological and histological changes in Tilapia zillii exposed to sublethal concentrations of the effluent of the Egyptian copper works. Acta Ichthyologica et Piscatoria, 29(2):73-80


United States Environmental Protection Agency, Office of Water Regulations and Standards, Washington, DC 20460 (1986) Quality Criteria for Water (EPA 440/5-86-001) pp. 150


The Chemical Engineer Mr Paul Nissianakis, who has calibrated the AAS methodology for copper in sea-water and bottom sediments, according to the internationally accepted standards and has provided the copper measurements.



Author: Dr. Panos Varvarigos
Freelance Veterinarian - Fish Pathologist, Athens, Greece.


Reproduction of this website (or parts of it) is illegal and strictly forbidden.
No rights can be derived from this website.


Every effort has been made to ensure that the information is accurate until the date of last editing. It is based upon the accumulated personal experience of applied veterinary work. The author cannot take responsibility for incorrect interpretation or any resulting consequences. The contents may be used as an educational guide and are definitely not meant to become a stand-alone diagnostic tool or operations manual.


Advertisements by Google